["Obsession" is such a harsh word. This is obviously just a wholesome, healthy level of interest. Heh, don't mind his private amusement at the startle.]
I will serve your afternoon tea in twenty-two minutes. [How's that precision for communicating "this is a set, non-negotiable time"?] There will only be so much time for truancy, unless you wish to forgo that.
[Not much time for your silly rides and cotton candy, in other words. This does happen to be the time Sebastian was planning on serving tea, but... it's convenient, since he'd also rather they go somewhere with no chance of people interrupting them already.]