How much time should I be spending on solving a puzzle?

I typically play play 30 minute rapid games and I definitely have to manage my time with a game that fast. I find that when I get into a position that I think needs a bit more analysis I find that I tend to make my “king of the hill” after 2-3 minutes. Otherwise I run out of time in the end game. When I am solving puzzles and I don’t fully see the solution I make my, “king of the hill” move at 4-5 minutes. When I look at how long the puzzles are supposed to be taking me it’s normally at least half the time of what I spent. Should I be focusing more when I do puzzles and trying to bring my threshold down to 3-4 minutes? My solve rate is currently around 75%

It depends on how difficult the puzzle is for you and if you "understand" the puzzle idea(s) at play, or if you are just trying to calculate only and don't see the concepts at play.

Generally speaking, it is better to take a little longer and to try to understand the puzzle. By "understand" it might be as simple as "I see this one-move Knight fork" or as complicated as a forced checkmate in 5; it all depends on the puzzle.

Ideally, you want to be getting down closer to the target time, but sometimes this is not realistic and besides, you'll naturally get faster at correctly solving puzzles and your overall experience and pattern recognition increase.

Solve rate of 75% is pretty high; mine is close to 50%, but even if it was around 60%, I'd say that would be fairly common. If yours is 75%, then you'll probably reach your true puzzle ability once your rating goes up more and you encounter tougher puzzles.

If you don't see the puzzle solutions quickly, then spending 3-5 minutes on it is completely normal though.