I do hope I can participate tomorrow...I could have stuff going on around the tournament time. How long do tournaments usually last?
Tournaments usually last for ~2-3 hours. This does vary with your performance, however. Losing in the first round = 30 minutes, while landing in the top 8 will mean that you'll have to set aside the full 2-3 hours.
That being said, leaving mid-way through the tournament without notice is generally frowned upon.