Well, you can set the timer to 99 hours, 59 minutes, 59 seconds if you type in the values, so it doesn't seem to make sense that 23:59:60 would break it. I'm really curious as to why that happens.
it looks like some default limits are in place for this. Here's what I found:
Max for seconds: 999
Max for minutes: 999
Max for hours: 23