It's white to play and mate in one of course.
The most difficult (?) mate in one move

I had a look, then went to set my clock, then after that it took me 37 seconds but I had already looked at the puzzle.
I looked at the mating net for like 15-20 secs and then got lucky as the first move i tried proved to be the correct solution.
Took a lot more time to look at all the other moves afterwards, I like your composition.

I thought it was too simple until I noticed the f2 rook is pinned. Then it took about 5 minutes to count up the 28 checks, and another 5 to see that only one of them works. I didn't worry about legality because I knew Arisktotle would take care of that.

1 minute 23 seconds. FIDE rating 1507 - however I have reasons to believe it is underestimated, for example tactics rating on chess.com is around 2200.

5 seconds. What did you mean, this is hard? It's obvious.
Does that only mean that you found a mate in 1 in 5 seconds? Or are you claiming that you verified that all of the other 27 checks were not mate in 5 seconds?

A minute for me. But that's because I've made a few of these myself too and know why it could possibly be difficult. (Yours has far nicer interferences though!)
I'll throw this out though (less elegant but maybe cute):
5 seconds. ? It's obvious.
Does that only mean that you found a mate in 1 in 5 seconds? Or are you claiming that you verified that all of the other 27 checks were not mate in 5 seconds?
No, I found a mate in one in five seconds. I wasn't talking to you when I said "What did you mean, this is hard," I was talking to Joachim.

Please post your approximative rating and resolution time but not the solution.
Took me about forty seconds. I think I was a bit lucky. I just started considering checks and asking myself if it was mate. The fourth one was. Rating here, 1450ish for blitz, 1550ish for standard. And I'll echo others, it's quite a nice composition.
Please post your approximative rating and resolution time but not the solution.