Ironically, I just cracked my screen today. Regular S6 with no case. I went for a run stupidly forgetting my key was in the same pocket as my phone. The weird thing is that the key was apparently pressed up against 1 spot on the glass the whole time and looks to have been rubbing on only that 1 spot (no other scratches to be found). But rather than just scratching the glass at that spot (which it did), it also sent cracks splitting from that spot in 3 different directions.
Got the phone on 4/9, bought Squaretrade insurance on 4/19, cracked the screen on 4/21. I'm thinking of waiting a month or so to put in the claim so they don't hassle me, but I suppose it depends on how much the crack bothers me. The other reason I'm reluctant to send it in is that it was working perfectly with none of the issues I've been reading about on this board. If I send it back, I suspect I'll just get a refurb that may be full of issues . . .
Woe is me . . . :-X