I read a handful of threads here and the go to answer seems to be 24 hours. Really, I just let the amount of rust decide. My legs weren't too bad - I think they were in for roughly 16 hours or so. Leg bolts and nuts for maybe 6 or so so, probably didn't even need that long.
I think the coin door was around 12, but once again that was probably more than it needed.
Lock down receiver was the worst - it was in a full 24-30. (Then 20 minutes or so in the over at 160) Came out great.
Made a PVC tube container as most people have. Works great for the legs and lockdown bar.
I went with a 3" PVC tube instead of 4" Two legs can be submerged at a time in a single gallon.
Found some plastic bins at Target that the coin door fit into really well. Minimal extra space, allowing the evapo-rust to fill the bin higher.
If you remove the hinge, you can just about submerge the entire door in a single gallon.
Quoted from Stoomer:
Make sure it's warm enough...Ken Layton schooled me on this recently - Evapo works much better over 60 degrees F. I tossed a whole gallon thinking it had been "played out", but it was probably just too cold in my shop(like it is in the winter) and I didn't know...c'est la vie.
Good point. Temperature affects the effectiveness. I did mine in the tub of a spare bathroom. If it's Summer time and hot out, I've seen people claim they've had legs done in a couple hours.