The Passive Wither option appears to have two lines with an option, defaulting to conflicting values.

I:passiveDecay.time=72000
I:passiveWither.time=-1

What do I set both to, to set decay to the proper values?

Vazkii, don't let them get to you.

first one is correct
ignore the second

So the second option does nothing? Ok then.

it's a leftover from old configs.