It's usually best to let Time Machine do its hourly backups. It was designed and optimized to work best that way, and will protect you best if you let it do that.
If you're considering this because your hourly backups are too large or degrade your Mac's performance significantly, there's likely something wrong. Doing backups less often is dealing with a symptom, not the actual cause.
If they're too large, using too much disk space, see #D4 inTime Machine - Troubleshooting.
If they're slow or hanging, see Troubleshooting item #D2 there.
Re-igniting this thread with my own variant on this which doesn't seem answered in those links:
My bottom line is I want backups but I don't want my disks spinning all the time. We all know hard-disks fail, and the more a disk is used, the more chance it has of failing. This would apply for both the one inside my IMAC and the external I'm using as the timemachine/backup.
I don't understand - this process seems self-defeating as I can't schedule less-frequent backups (reducing the chance of disk failure) without a third party tool/scripts (which I don't want to use)...
Thoughts or corrections?
. . .
We all know hard-disks fail, and the more a disk is used, the more chance it has of failing.
That doesn't seem to shorten the life much. Most decent-quality drives are built to run most of the time, or 24/7, so only spinning up once an hour (and sleeping while your Mac does), shouldn't be a problem.
Apple has resisted all requests for options to alter the interval since Time Machine was first released with Leopard about 5 years ago. So it seems clear they think the benefits of hourly backups are worthwhile. But if you think it's really significant, add your vote here: http://www.apple.com/feedback/timemachine.html.
One alternative is to turn Time Machine OFF and do manual backups via Back Up Now. For most of us, that's much too easy to forget.
Or use a scheduler, or another app.