Clockwork Prince question

Wasn't the issue with who the demon was, not that he was in the Pyxis? I think I thought this too when I read it but I think there was some other reason that cause Magnus not the think about it...

I think Will didn't tell Magnus all that happend but rather that he needed to find a demon. So Magnus couln't have told him early about the curse.

I doubt Magnus actually knew as even I myself thought that the Demon that Will wanted had done something, I never would have thought what it could have been or that it was at all a curse. But then again if Magnus did figure out what was going on...he is after all a warlock, not the most honest dealing being. He seems to have a good heart, but since when is evil ever anything to be trusted? H emight just have been entertaining himself...or he really did not know...

The ability to cast a curse depended on how long the demon was in the Pyxis, remember? And Will couldn't tell Magnus that because he couldn't know, Magnus only pieced it together when the demon told him.