Is it possible to have a dweller exploring the Wasteland for more than ~3 days?
Solution 1:
The amount of time that a dweller can spend in the wasteland is directly effected by said dweller's luck in finding items, as 100 items causes the dweller to turn back. The longest time someone's dweller has stayed in the wasteland is about 90 hours, according to www.steamcommunity.com, and there is no absolute way to extend the time in the wasteland. That being said, the time in the wasteland is dependent purely on luck.