Felix takes the moments of silence to gather himself. He's honestly surprised when Harrow doesn't react, though it's a puzzle he can't afford to stop and think about. It's time for the delicate business of negotiating, and he has to stiffen his resolve and get down to it.

Harrowheart must be able to leave you in a safe place and travel apart from you, he says, trying to identify each element in his thoughts in turn, nice and clearly. The better to notice which of them is about to incite the most resistance. No farther than he can travel through one portal, for no longer than a year in his own realm's time, without any attempt to steer his will when he chooses to do so.

The 'how long' aspect is the most flexible here, one reason why he's made a fairly audacious request there.