Bamboo Bar down by Jomtien beach used to be open but the guys there didn't really interest me.As far as I can remember, none of the gay go-go bars ever opened in the afternoon hours.
There's always tons to do in Bangkok during the day - a visit to Golden Cock followed by a long sex sex session back in the room, a long lunch, a trip up the river, shopping at Siam Paragon, or just wandering around.
Pattaya is a different story. Until I found a regular friend, I'd go for a massage and then have nothing to do until the evening.
The way things are at the moment - and possibly into the future - it will be a while before bars attempt to open during the day.