Knowing when you've reached your (time) limit

I made a mistake playing in a SNG recently. It wasn't a mistake that would occur to everyone right off. It didn't have anything to do with what plays I made, or what stakes I was playing for, or anything like that. My mistake was, I got into a tournament without making sure that I had time to see it through to the end. I had a commitment Sunday afternoon that required me to be somewhere at a specific time. I registered for an on-line multi-table SNG about two hours before the time when I would have to leave for my appointment. I thought that I would have enough time to finish the tournament, even if I made it to the final table. Well, I did make it to the final table, but when I got there I only had about ten minutes before I had to leave. As a result, I had to rush my play and ended up busting out on the bubble, missing the money by one place. I didn't make a particularly bad play when I busted out, I don't think. I just never should have got into a multi-table tourney knowing I had a commitment that could conflict with it. If I hadn't busted when I did, I would have been stuck there and would have been late for my appointment, which I never like to do (especially because I would have made the rest of my family late too). I won't make that error again. Next time I'll play in a regular game that I can leave whenever I want. :-)