From weaknees.com, a site that offers a bunch of Tivo related upgrades and accessories, a tip that save your eyes and your thumb:

Every TiVo can do a 30 second skip – you just have to enable it.
Here’s how you do it:

1. Start playing any recording.
2. During playback press:
   Select – Play – Select – 3 – 0 – Select
3. You should hear three bongs (if you don’t have the TiVo sounds disabled), and you’re done.

Your “skip to beginning/end” button (the arrow pointing to a line)
is now a 30 second skip button. During fast-forwarding or rewinding,
the button will still “skip to tick.”

For the most part you can press the skip button about 4x’s and you’ll be reasonably close to the next segment. I’m not sure what the usual commercial break is, but in the short amount of testing I did, it was anywhere from 2 minutes to 2.5 minutes.