There are other threads about Bangkok as a visa run destination. I think it usually takes five days to process there. The easy way to get a flexible return is usually to pay more, or at least not get a discounted ticket.
You take your paperwork in one day and go pick up your visa the next weekday. If you want to go somewhere outside Bangkok for the weekend after handing in your paperwork on a Friday, remember the Bangkok visa office will have your passport and in Thailand most places you stay at will ask to see your passport.
Check out KLM on the net. It’s fairly easy to organize flights through them if you have a credit card.
It is possible to pay an express fee and get the visa issued the same day. I did it in Bangkok in May this year. Otherwise you apply in the morning and pick it up in the afternoon the following day.
Thailand has quite a few public holidays. Do check to make sure that the office won’t be closed on any of the days you plan to be there.
Also as mentioned above do a search and I’m sure you will find lots of info.
I was in BKK last spring on a visa run and got it done the same day. I would warn though, that you should get there early; at least 20 minutes before the office opens. I got there exacly on time and barely got processed before the noon cut-off. You can also save a lot of time by checking what copies you need and do them before you go.