I am having difficulty with the ferry website. Can anyone tell me how much time to allow for the ferry ride from Hvar to Dubrovnik? Or, is there a better way to get from Hvar to Dubrovnik? We will be there in September.

the ferry schedule bet. Hvar to Dub. is found on the j. ferry schedule under "international routes." I'll be taking this route in about 2 weeks, which is considered the low season, so that ferry route only runs 2x week. I don't know the frequency in Sept. You may know this, but the main port for Hvar is Stari Grad, and not the town of Hvar.
for real stumper questions re Croatia, I've been emailing atlas travel there. let me know if you want a contact email address. they've been great.

I'll be going to Hvar in September. I called the Croatian Tourist Board (212.279.8672) to get ferry times from Split to Hvar (I had problems with Jardolinja website also)

The only other way (I can think of) from Hvar to Dubrovnik would be Hvar to Split (2 hours) then take a bus from Split to Dubrovnik, which is about 4 hours

I've been struggling with getting ferry times from Dubrovnik to Hvar and discovered that the ferry in May runs twice a week. It is much easier to get to Hvar from Split.

I finally decided to get an extra plane ticket so that I can take the ferry to Hvar from Dubrovnik and then at the end take a ferry from Hvar (Stari Grad) to Split to fly out of Split. The ferry connections to Split are 2 to 4 times a day instead of the twice a week to Dubrovnik (and around 7 hours). But times vary with the day of the week and the time of year so be sure to ask the ferry company for all the relevant info. I had trouble getting the ferry web site to work. Best of luck.

Jadrolinija's website is very confusing. Like so many other companies, they've tried to be too clever - it was much simpler when their website displayed a simple timetable for each route.
The coastal ship runs twice a week from October to May, but is more frequent in summer. In September, there are sailings from Stari Grad on Mondays, Wednesdays, Saturdays and Sundays from 3 to 21 September, then on Tuesdays, Thursdays and Saturdays from 23 to 27 September. The ship leaves Stari Grad in the morning and usually gets to Dubrovnik mid-afternoon. The ships have restaurants and the scenery is superb - it's worth being on deck when the ship calls at Korcula. From Hvar town, there are connecting buses to Stari Grad (make sure you get the one to the ferry terminal, "trajekt", rather than the town of Stari Grad) or it's not too expensive by taxi. Advance reservations are not needed and the ships will not be too crowded in September.