I am talking about a SP Swing, which is basically a 2 pt mount system. Since it would be "sitting" with just the mains intact, wouldn't those 2 end mounts keep the frame somewhat from any damage to the frame?
I am no expert on this issue, so take my words here with a grain of salt. I'm sure there will probably be many who refute what I say, but this is my take:
It's the pulling tension that REALLY puts stress on the frame. Merely mounting the frame shouldn't really be putting much (if any) stress on the frame. I think this is especially true of suspension mount systems. And If you watch yulitle's video on 6 point mounting, he indicates that the supports should be "just barely" touching the racquet, as the point is the keep the frame from going out, not to "push the frame in."
It seems to me that merely having a racquet mounted shouldn't put much stress on it at all. Maybe a little bit with some of the two point press down systems, but even then, if you aren't over-tightening, I don't think there is much stress on the frame just from mounting.
That said, there is tremendous stress being exerted on the frame during tensioning. That much is for sure. This is why the frame needs to be securely mounted.
If you've done the mains, then you've tensioned in one direction, and there is forced being applied to the frame for sure. At the point when the mains are done and the crosses haven't been started, the frame may have actually narrowed (or elongated) a bit. This is normal and once the crosses are done -- assuming you haven't changed the tension between M and X too much -- it should even out in the end.
Is it bad to leave the mains sitting for a long time before doing the crosses? Eh... it's probably not as bad as some might have you believe. But then again, I wouldn't recommend leaving it sit for an "extended" period of time that way. 30 minutes probably isn't the end of the world though.
But again, take my words with a grain of salt, because, to be brutally honest, I have no idea what the hell I'm talking about, and I'm basically just giving my best guess! ;-)