Approximately, 3s on clock is worth a pawn.
How much are the pieces worth in units of time?
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You can wait for a mating piece but shouldn't wait for anything else. Moving fast can usually cure most problems.
While you are certainly right, it is generally NOT wrong to assign piece values to time, as time is integral part of bughouse. Your described situation is fairly rare, it is similar to chess situations where pawn is better than rook etc. So sure, if you have better position and more material on both boards, then time doesn't matter at all. However, this is exception.
In a bughouse game, everyone moves fast. There is a chance that you blunder a knight/bishop or worse, a queen just to move fast. Would it be worth it to blunder the pieces just for 2-4 seconds on the clock?