Yes, time of day can help you to keep your rating as high as possible for as long as possible. 5's groups typically aren't sold as much as 2's and 3's, I've found. A 3's group will easily hold all of your 5 characters -- just play 2 sets of 5 games on each group of 3.

The trick is to find out when other people are doing the same thing that you are. For my server, that means late at night. You're going up against teams who are expecting to lose because of their sh*tty gear - so why not try to win? If you face these sort of guys, you can easily get your team rating at a stable 2k and your personal rating up some too, if you're lucky with the queues.