Honestly, who let Tony be a Sentinel? He's a terrible influence. (And more likely to get his Fatemarked into trouble than out of it.)

Tony almost says 'right now,' but that would definitely look suspicious. After a moment of thought, he says instead, "Tonight. After dinner. We can meet up in the cafeteria and leave together after we've eaten. It'll look like we just got to know each other and decided to hang out."

It's a little risky to be seen leaving together, but Tony thinks that's less likely to arouse suspicion that they're up to no good than them slinking into each other's rooms. If there are hidden security cameras, it's better to act normal and maintain plausible deniability for as long as possible.