There are 7 monitors that keep track of system tests.
Some of those tests take a considerable amount of drive cycles to complete.
The Evap system is quite involved so can take some time.
Reason they take various amounts of drive cycle time is the testing is done under many conditions that you may not present during your driving.
So the 50 mile answer is not always the last word.
Until 'all' the monitors are reset you will see a code 1000.
This code is only related to the monitors and not a direct trouble indicator as is has no discription like fault codes have.
Good luck.