A couple of minutes for me- I had the right idea for the start 1.Nd6 followed by Ne4 and Bb5, but couldn’t immediately solve the problem of the black king escaping to the b4 square when Bb5 is played- then I noticed that after 2.b4 black is forced to take the pawn blocking the square with his own pawn. This is actually quite a nice puzzle for being nothing but forced only moves for black.
15 minutes
1. Nd6+ Kc5 2. b4+ ab 3. Ne4+ Kc4 4. Bb5#
4 minutes and 40 seconds
A couple of minutes for me- I had the right idea for the start 1.Nd6 followed by Ne4 and Bb5, but couldn’t immediately solve the problem of the black king escaping to the b4 square when Bb5 is played- then I noticed that after 2.b4 black is forced to take the pawn blocking the square with his own pawn. This is actually quite a nice puzzle for being nothing but forced only moves for black.