I do have a twitter account, but nowadays I don't post anything there. I don't have that many people listed there, so I don't think it's a good method to promote anything. But maybe it works for you guys, hehe.
Best times are: 9.30am, 1pm & 7pm.
Makes sense, when people arrive at work, lunch time & when they get home just after dinner time. Where do you go? To the computer.
3-5 Times a day is a good number. Nothing more than once an hour...