Had an objective: have an explorer explore for 10hrs.

He was out there 12+ hrs and took 6+ hrs to get back and no lunch box for me idk why

if they are already in the wastelands before the objective started they don't count. You have to send a dweller out after you get the objective you can tell as it counts the hours of as you complete it. if you don't get that they are not counting towards the objective.

I had the objective for a few days before I sent him out