You won't be able to bring a character on a mission if they're in the middle of a task, and considering that the tasks can last up to two hours, it's more efficient to spend your fuel first.
Ngeke bakwazi ukuletha uhlamvu elizimisele uma siphelela phakathi umsebenzi, futhi ucabangela ukuthi imisebenzi kungathatha amahora amabili, kungcono iyashelela ukuchitha uphethiloli wakho wokuqala.