Sirius had to be sensible in this case. This sort of thing could get out hand very quickly and he didn't know about Remus, but he didn't like to be rushed by a time limit. Besides, a bit of teasing could be fun. He would show Remus.
"If that's what you would like," Sirius replied casually, reaching out to help Remus with the unbuttoning. "It would be interesting to see how far out we can go."