12 days in Vietnam Jan/Feb
 

The last country on our 9 week SE Asia trip will be Vietnam. We understand that the highlights are
Hanoi, Sapa mountain villages
Ha long bay
Hue
Thien Mu Pagoda, Minh Mang tombs
Imperial city
Hoi An
Saigon
Dalat
Ha Tien

We will have seen a lot of temples. My husband (not myself) is a bit of a motorbiker, so we could do a short motorbike trip.
Any thoughts on amount of time in each place or other places to go would be much appreciated.

Thank you

Here is a link to our blog of our time in Vietnam https://accidentalnomads.com/category/vietnam/ which may provide some ideas.

With twelve days, I would suggest just the north and south and miss the centre. I really like Hue but don't think you really have enough time to do it justice.

Hanoi needs a few days. Sapa and Halong I would avoid, simply because they are over touristed these days and instead look at Ninh Binh - Mai Chau and beyond. Possibly consider a trek in that area if that is your thing.

I am an experience motorcyclist but would avoid riding one myself in any of the cities (although Hue would be better than most, or possibly Hoi An) . Check the legal requirements as I believe you still need to get a Vietnamese license (impossible in the time) or at least in International License. Easy Riders allow qualified rider to ride there bike (250cc) otherwise it is likely to be Honda Dreams etc.

For allocation of time, iwoudl probably go with 7 days north - 3 in Hanoi and 4 in Ninh Binh - Mai Chau and 5 south split between Saigon and the Mekong Delta.

If you wanted to add a additional area then Hue or Hoi An. But to get one full day in each of those places, you would need two nights apiece.

The other approach would be to spend the entire time in either the north or the south. In which case you would be able to see everywhere at a much slower pace and in more depth. ( always a good idea in Vietnam)

You need to be aware of the TET celebrations in February, which might restrict any domestic travel arrangements you intend to make...

https://publicholidays.vn/lunar-new-year/

Accommodation also fills up quick, and prices might increase for that 15-21 February period.

Me and my wife were in Hanoi on 10-15 February this year, and it was quite cold until about 1000 each day.

Hanoi, Sapa, Ha long bay, Hue, Hoi An, Saigon, Dalat and Ha Tien. Too many places but you have only 12 days - Too rushed!
Hanoi (2 nights), Halong Bay (1 night), Sapa (3 nights - night train to Sapa and back Hanoi), Hue (1 or 2 nights), Hoian (At least 3 nights), Saigon (2 nights), Mekong Delta (1 or 2 nights). You should skip Dalat because Dalat is the place for relaxation NOT a MUST SEE place!

I think you can explore Viet Nam 9 days with: 02 nights in Ha Noi, 01 night in Ha Long, 01 night in Hue, 01 night in Hoi An, 03 nights In Ho Chi Minh city and rent motobike Vespa to explore Ho Chi minh city

You've listed what someone else considers to be must-see places. What do YOU consider to be must-see places.

You have way too many places on your list for 12 days. Do some editing and you can have a fine trip to VN.If you try to do all of that in your short time you will feel frustrated and exhausted and will come home with no sense of the country, the people, the culture.