I noticed that when I close the default fuel page the fuel truck goes away immediately.
That's normal. The time it takes for the refueling to happen, is the amount of fuel you loaded, which is of course the difference between the total fuel you had *before* opening the page and the fuel you have *after* closing it, multiplied by a factor of seconds * gallons of fuel loaded, which is a setting that can be also customized via an .INI setting, as explained in the manual.
If you open the page and then close it, without adding any fuel, the fuel truck will go away immediately.
Where is the option to disable the FSX fuel page poping up?
As I wrote in my previous message:
We might add a switch to disable the default fuel loader with some airplanes with an upgrade.
So, it's not there yet.