According to the UA international checked baggage website (http://www.united.com/page/article/0,6722,52482,00.html) checked baggage cutoff, even for international flights, is 45 minutes. I wouldn't cut it nearly this close if I were you, in fact, most international flights, if I'm not mistaken, board 45 minutes prior to departure.

2 hours is indeed a recomendation, and I would pretty much follow it for international. I'd rather have an extra half hour than be late by a few minutes.