If I were you I would just fill it up now and calculate how much fuel you added (can always weigh the remainder of the last 5 gallon can to calculate what's left). It is a PITA to run out and have to bleed air from the system in the field.
Please don't run your diesel dry!!!! Some injectors and or pumps do not take kindly to that. Think about it, the new "DRY" fuels are hard on these items, pumping air is not any better for lube. CJ