The 30 days will be added on to the current expiry date i.e. the new expiry date will be 90 days from when you entered Thailand, and you can extend it now - you don't need to wait until the expiry date of your 60 day tourist visa
Last time I crossed the border (I guess it was after 8:30 am) I spent most of the morning waiting to submit my paperwork at the Thai Consulate....I'm just trying to get there a bit earlier to try and reduce the time spent waiting at the Thai Consulate, although I don't think I'll cross the border at 6 am, maybe 7 am or 7:30 am?