Ehhh.The trouble with dropping timestop is twofold:
1. We told Mami we were just going to talk with Homura, not go anywhere or do anything dangerous.
2. We told her we'd be back instantly after that talk.
In retrospect, this was a poor decision caused by uncertainty over whether or not we were actually going to hunt Sasa, but we'll have to live with the constraint for all but immediate life and death situations. Even then, it's timestop - "immediate" is indefinite. If we have to break it, we should go back and bring Mami in first.
As for Sasa, if she's contracted, we should come back later, perhaps with Kirika for antimagic or Mami for extra backup. If she isn't contracted... leave a note floating in timestop, right in front of her?
Literally leaving a note doesn't seem useful.
If she isn't contracted, it's a quick 'hi, bye, do you want to hang out sometime?' If she is, things have escalated to the point where we may want to bring Mami in anyway.