Magic spell trap CR question

[Eladrinblade]

In a dungeon I'm designing, there's an underwater tunnel with a summon monster spell trap. It's summon monster III, and it summons a fiendish crocodile. By the rules, a 3rd level spell magic trap is CR 3, even though it only summons a CR 2 monster for 5 rounds...

So, is there justification for it being CR 3? I guess if the trap is undetected, the PC(s) won't be ready for it, but still.

[Fizban]

Which is more challenging: one crocodile, or literally infinite crocodiles?

[Eladrinblade]

It only summons one crocodile, unless I'm missing something.

[Fizban]

Maybe if it's a single use trap, but this would be the first time I'd ever seen someone actually make a single use trap in the history of ever. If it's the standard automatic reset trap, it summons a crocodile every time someone triggers the trap, as often as they do so unless you impose a set delay of your own. If one PC enters the area, that's a crocodile. If another PC then moves forward to help fight, that's another crocodile. Every time someone enters the trigger area, boom another crocodile. If they exit the area and return, more crocodiles. Disable the trap? Suppresses it for 1d4 rounds, then more crocodiles.