I agitated for the first minute, then just let it sit untouched for 1 hour. The scan was hard because of the dark red/orange color of the negative. There is some posterization but I think (hope) that is a scanning artifact. (I don't have a particularly good scanner). Dealing with the remjet backing wasn't as hard as I feared, just a bit messy.
The backing dissolved and came off quite easily actually; I am wondering if the fact that it was stand developed for an hour helped? (Or something specific to Rodinal; I'm not an expert so I'm just speculating). Also, the film had an expiry date of around 2008 IIRC; from what I've read the older the Kodachrome, the harder it is to remove the backing.