Best farming method I found was running mission 15 (get it originally from kid gohan after completing Frieza Saga)
One of the Ultimate Finish conditions is to finish the fight in 3 minutes which is very easy to manage once over levelled. Then you have a chance of spawning a time patroller who jumps into the fight.
Frieza can be defeated in around 1-2 minutes or even less than a minute with a beefy character.
Pretty good for experience grinding too, grants a fair bit with multiple quick runs.