When was Dana planning to ambush Roy in chapter six?

Dana's planning to ambush Roy after school. He's a real bully and hates the fact that Roy stands up to him. As far as he's concerned, Roy's cruising for a bruising, and it's just a matter of time before he gets what's coming to him. In fact, as Garrett tells Roy, kids at school are actually taking bets on how many times Dana will beat him up. One day, Garrett tells Roy that Dana will be waiting for him after 7th period. He's going to snatch Roy before he has the chance to make it to the bus.
After history class, Roy sticks by Mr. Ryan, hoping for protection, but he soon finds himself all alone in the halls. Then, as Roy walks past the janitor's closet, Dana suddenly jumps out and drags him inside. Dana proceeds to give Roy a good beating; he's been waiting for this moment for a long time. After what seems like a lifetime of savage punches and tight, crushing bear-hugs, Roy's saved by a mysterious intervention. Seemingly out of nowhere, someone—Roy doesn't know who—lifts the bully right off him, allowing him to make a run for the nearest exit.