I'm interested in knowing how long it may take to achieve equal voltage (or 0 current) in the above example of 4.2 hooked to a 3.4 volt.

Oops, just finished reading the answer, Thanks.

I have observed something that I can't quite figure out and it occurs with paralleling packs and also after chargeing the paralled packs.

That is after leaving them connected to each other (on charger or off) for hours. Upon disconnecting them the voltages are not equal.
Any idea why this may occur? I've noticed it on various packs 2p, 3p equal and unequal capacity packs.