The fuel bowser takes everything in strict rotation, so that if you see an An-12 on the ramp you just know you are screwed! My Twotter takes 15 minutes to top off but they drive right past to spend an hour pumping kerosene into that dinosaur.
A lot of local fuel suppliers see bigger bucks in the larger types and will ignore your requests for fuel in order to be ready to refuel a one off large aircraft just passing through. Their little eyes sparkle at the potential for gravy while ignoring the fact that the local operators are their bread and butter as they require fuel every day while the big ship may pass through once a month. Suppose that's the price you pay for having to get your fuel from a local monopoly, probably owned by some minister. Of course, screwing up the little operator's schedule means nothing.
A little competition may improve things but it's more than likely both suppliers would become slow and useless. Entropy is a powerful force in Africa.