Which type of trap have u got? Those plastic ones with a partition or like a net?
If it's those plastic ones, I wont leave them there for longer than 2 days, coz there's not much of a water flow in there, resulting in oxygen starvation.
If it's like a breeding net, then u can allow urself more time until u've set up a fry tank ready for them.
How many frys u have there?