The temps can vary quite a bit in a single day depending on current and dive site. I have been comfortably warm in a 2/3 full suit and freezing cold in the same suit a couple hours later. However, most dives were on the comfortably warm end.
I don't believe there are any direct flights. I have been advised not to try the NAM flights, they are often cancelled.
Do not believe Lion Air's second flight of the day to Alor. The only one that actually flies is the Wings Air flight at 08:15 - IW1943. You can sometimes book a later flight that seems to be a better connection - it never actually flies and Lion Air will rebook you on some interesting itineraries - ask me how I know. A couple of years ago it took me three days to fly to Alor, overnight in Surabaya and then overnight in Kupang - instead of the one day I had booked.
To get to Alor from Jakarta with one stop in a single day you need to leave at 2:00 AM. There are no good options from Bali to Alor. You can get there, but you fly through Jakarta.
I find that staying overnight in Kupang is the best way to get to Alor. Hotel La Hasienda is close to the airport and an interesting place to spend a night.
