I'm pretty sure that I remember that this is configurable, but you have to have a network interface on your TiVo to do it. I can't find the docs right now, but it seems like you can't add more options, but you can change the options that exist. And you can't get it to start late, but you can get it to start a negative number of minutes early, which is the same thing.

Unfortunately, I can't find that documentation now.