You will lose two whole days getting to and from Koh Phi Phi. Bangkok has so much to offer that you shouldn't shorten your stay there. Because of your limited amount of time, consider Hua Hin which is a 2-3 hour drive from Bangkok. Not as exotic as Koh Phi Phi perhaps, but it will give you more beach time. You will also eliminate the variables involved with flying - a delayed or canceled flight could mean missing your flight to Vietnam.

You will not lose two whole days going to Phi Phi....if your budget permits. In fact, I would go for exactly what you have proposed. We regularly take breakfast in Bangkok and have a swim at Phi Phi before lunch...no problem.
Fly into Bangkok and head straight for Phi Phi.
Speedboat transfer is the key to optimising your time at Phi Phi. You can go from Bangkok to Phi Phi in about the same time time that it takes to get to Hua Hin. Around an hour to fly from Bangkok to Phuket and 90 minutes from Phuket airport to your Phi Phi resort check in.....right on the beach !! Easy!!
Bangkok is a unique and wonderful city......but for many....like me...it has to be in short spells.
Phi Phi too, is unique, and if you are a paradise beach type of person, then head for the north east coast away from Tonsai Village.
There are many on this forum who will advise against visiting Phi Phi (most of whom have never visited or at best done a day trip), but if it has attracted you, and you are a beach/sea/snorkel/tropical paradise kind of person......don't miss it.

I think your idea is good, op, if u don't mind a hit and run type of travel. Id rather stay all 6 days in bkk and do phiphi on another trip. Good luck.

perhaps craig stretched it just a bit but he is not far off... i would not go to two places quite honestly....i would stay at an hotel in bkk with a fabulous pool area (marriott resort and spa, royal orchid sheraton, nei lert, sheraton grande to name a few) and spend the whole time in bangkok... spending all this time in the transfer process is just time wasted...

i expect you will get some beach time in VN as well...

While Bangkok offers a lot to see and do, and you may be perfectly happy spending all your time there, I think it would be easy to do a city/beach in Thailand if you pick the right beach location. I don’t think the Phi Phi is the right location, as it has no airport and requires further boat transfers. This can be a pain on the inbound and outbound. I would suggest Krabi, which has its own airport. You can fly non-stop to Krabi from Bangkok in just over an hour (including an 8 am departure that would IMO work well and give you a full day in Krabi). Krabi is stunningly lovely too. (Phuket of course if another option, but of the two, I prefer Krabi. Less developed and good beaches right there, as opposed to Phuket where the really good beaches are off the island.)

Be a little careful of rain in November on the west coast. See weather websites and guidebooks and make sure you are OK with the possibility. Late November would be preferable, as that is just the tail end of the rainy season.

Thanks for your advice everyone (and on a long weekend!). I am a bit concerned about the transfer times but I really would like to do two locations just to get a little taste of Thailand other than the city.

I confess I'm not a huge beach person, but I have never in my life seen a beach paradise like the pictures of Koh Phi Phi. Who knows, maybe I'll be converted. I know people who have been there who have raved about it.

We would arrive in Bangkok around 11am, so if we headed for Koh Phi Phi right away, we still might not make it until evening due to flight/ferry schedules. I think I'll look into Krabi. What does everyone else think of this idea? Any other location suggestions?

and in fact you might not make it that night....

krabi is an excellent idea....do not stay in an nang unless you want a very touristy almost run down area....stay where the sheraton on sofitel are located....if you can afford it the amari vogue is fantastic... and small

the sheraton is very nice...

Phi Phi is indeed lovely, but don’t be misled. There are many gorgeous areas on that coastline. You are somewhat spoiled for choice. (I have this same issue with Switzerland, where I used to live, in that all tourists go to the Jungfrau when there are tons of stunning mountain areas elsewhere.) Khao Lak is another gorgeous place on the coastline north of Phuket amd would be a great spot as well.

My personal view is that I would not want to go right to the beach from Hong Kong. I would save the beach for the end to really relax, esp after the craze of Bangkok. I also don’t think you could get to Phi Phi from Bangkok on the same day unless you hire your own boat, because from what I see the ferry only runs at 9 am and 2:30 pm, and you could not make either ferry. You could get to Krabi or Kha Lak, as you can drive from airports to hotels.

The only way you could get to Phi Phi on the same day is if you take one of the non-stop Cathay flights directly from Hong Kong to Phuket. The flights arrive at 10:30 am or 11:30 am into Phuket. If you can change your flights to skip Bangkok on the inbound this may work. If you fly directly to Phuket, you can also drive to Khao Lak (north) or Krabi (south) from Phuket airport. Takes about 2-4 hours depending on where you are going. There is ferry to Krabi, but it is not direct and will take longer than driving. There is also a 2 pm CX flight to Phuket from Hong Kong which would work for getting to Krabi or Khao Lak on the same day if you drive, but not to Phi Phi unless you pay for your own boat, see below.

You can also fly to Krabi from Hong Kong, but this will require a change in Bangkok. However the overall travel time is only 5 hours (including a short layover in Bangkok of about an hour), which is not bad and would probably be the best choice if you want to go to Krabi first. There is a Thai Airways flight which departs Hong Kong at 2 pm and arrives into Krabi at 6 pm. (Thailand is an hour behind Hong Kong.) This would give you the morning in Hong Kong, as you would not need to leave for the airport until Noon. (I live in Hong Kong.) From Krabi airport you can stay in Krabi (short drive) or go to Khao Lak (longer drive).

Otherwise, if you can’t change your flights and are committed to flying to Bangkok with an 11 am arrival, I think the earliest connection you could make would be the 2 pm Bangkok Airways flight to Phuket or the 1:30 pm Thai Airways flight to Krabi. So you will have about a 3-hour layover sitting around Bangkok airport. You will arrive into Phuket or Krabi at like 3:30 pm.

If you go to Phi Phi, once you arrive into Phuket, you will have to get to the boat pier and then take a boat. You will have missed the 2:30 pm ferry, so will have to hire your own boat. So add in time for finding a boat, haggling with the captain, etc. Plus you have to pay more than you would for the ferry. Door to door I think you are looking at another 3-4 hours at least to get to Phi Phi from Phuket Airport. For Krabi, you may be about an hour drive to your hotel, this will all depend on what hotel you choose (but at least a car to the pier and then a boat ride won’t be necessary.)

If you go to Bangkok first, then you could be at your hotel by 1 pm and could actually get in some sightseeing on your first afternoon.

I don’t know your budget for hotels, but in the Phuket area, you might look at the JW Marriott Khao Lak or the really fantastic Ritz Reserve Phulay Bay in Krabi.

I guess I should also add that if you are not a beach person, then perhaps going to northern Thailand (Chiang Rai, Chaing Mai) might be more interesting to you. Or consider going to Ankor Wat or Luang Prabang.