Is it possible change desktop theme In each hour
here I wrote you some scripts to do random settings using gconf.
Hope these help you.
Instead of writing a bash script you could do this all with cron. And if you're not a bash expert I'm guessing you're not a cron expert either so download Gnome-Schedule from the Ubuntu Software Center. That's basically a GUI for working with cron. Then just setup a task to run every hour that includes the following commands (you'd need a separate task for each command but they could run at the same time.
Important Note You'd need to make a separate task for each time you want the theme to change AND for each different theme it's going to change to using this process. Thus you'd make a task that runs every day at 1:00 to change the theme to Theme1. Another process that runs everyday that runs everyday to change the theme to Theme2, etc. The best way to do this would be to write a script but this would be an easy workaround.