In the past it was usually the morning or mid-day of the due date that the votes start and threads close...we try to aim for 5 days of voting before the end of the month.

A hard and fast time is hard to predict because we're all hobbyists with day jobs, so having a CL or me here to close the threads and start the voting at a hard/fast time is not something we can just schedule really. I'm sure if a few hours makes the difference between win/lose or post/no-post some allowances can be made if a pm is sent to the CL who ups the vote thread.