we mine likes it long and deep but wait a bit and you might get the correct answer
an hour long and at least 7" deep.
Short and thick will do the trick.
Actually this the correct answer to your OP. I did it on mine earlier in the year. The objective is to force the plastic casing which house the **** flaps er...I mean blend flaps apart to prevent them from snagging.
I'd say about 20 minutes and if its a bit short then wiggle it![]()