This puzzle has a target time of 53 sec (1660 puzzle) and its mate in 13...

The eye is drawn to R takes first, because it avoids losing the B to check. So you're going to spend a minute evaluating that. So then you play pawn takes but you don't actually know if it works. If it doesn't work then you seem to have dropped the exchange.

Black is already two pawns down, apparently with no good defensive moves, so as black you know you have to try for mate or you lose. So you look at R takes first, because the eye is drawn to that. But then you have to spot Ra8. I think that looked correct. 

If you see that quickly then you can sort of guess things aren't going to work out, and that you have to play pawn takes. So in a blitz game you'd play pawn takes quite quickly but this is a puzzle and I think you should do it not just based on a guess. OK, If I was on form I could do it in around the target time but on form I'm a strong player, so that's why I think this is aimed at far stronger pleyers than I am, if that's the target time.