How rapidly does the oxide form on aluminum? Seconds? Minutes?
Hours?

I don't have it handy but Boeings BAC 5555 spec for anodizing specifies
something like less than 30 seconds between tanks. The oxide layer forms very
quickly. Aluminum is a very reactive metal.

If all you want to do is make a fuel tank just pop-rivet the thing together
with enough rivets to hold the thing together and seal the joint as you rivet
with Pro-Seal. It stands up to the fuel just fine. The BD-5 wet wings are
made this way and don't leak if built with a bit of care.

For structural bonding of aluminum there is no substitute for the proper
anodizing process. If properly anodized, per BAC 5555 or similar, the parts
can sit on the shelf for a long time before they are bonded. For us "poor
boys" that just want a beter bond on non structural parts look up the FPL
(Forest Products Labrotories) etch. The only problem with this is how to
dispose of the left over Chromic acid.......