Great. Keltham didn't realize he was giving that away based on duration - should've realized, some spells he was reading had similar timings per level - but too late. "Over soon enough, then."
This next part is embarrassing. But if anybody catches you covering up an embarrassing mistake, that's much more undignified. And if you do it by violating something you were deontologically obligated to do, that is a lot more serious. So it doesn't particularly occur to Keltham not to do what he does next. He owes somebody a favor, and so he must -
"Also, and I'm sorry about this, your names all sound unhelpfully similar in my native language, there's two of them per person, and you don't wear convenient labels stating them so - can somebody else say what's her name, again? So I know who it is I owe a favor?"