It starts counting your bugs captured after you get to the 4th stage. But I discovered you can pull the bugs out of your inventory and put them back in, and it will count them. You can continue sleeping in a tent after you've come home, and that counts too.
@Brian_Z I could swear that insects caught were counted retroactively in one save years ago, but not the last couple of times I finished Outdoor Retreat.
Thanks for confirming that!
Removing and adding back items to a sim's inventory is fine for casual games, but it's a rule violation for this forum's tournament and dynasty challenges.
At least my sim will have 5 days to collect 15 insects. Mixed blessing.
I've completed the Sleep 5 nights in a tent for at least 3 different challenges. It's been a slog every time.
Once I tried to complete the goal with a sim who had the Never Weary trait, LOL. Had to redo Outdoor Enthusiast with a different sim.