When is it too much homework?

Rylee was working at the table and Hanna was working on the computer, both doing their homework. I left Rylee at the table writing letters and went to help Hanna, right around the corner in the other room. I was gone about five minutes before heading back to see if Rylee needed help. It was strangely quiet as I rounded the corner and there I found her sound asleep! So sound asleep that she didn't even wake up when I picked her up from the chair and laid her on the couch. These kindergarten days sure can be exhausting!