So hypothetically speaking, what would happen if it rained about 20 mins after putting on the 2nd coat?

Stupid me, forgets to check the weather, now a thunderstorm is coming

 

Second coat of what? A quick detail spray, or Z2/Z5/etc.?

If the latter, have you already wiped it down, or is it still drying on there?

If you've already wiped it down, then it shouldn't be a problem. It needs time to cure, but it's already dry and should be able to repel water.

 

I already had a coat of z5 just finished putting on a coat of z2 and it started to downpour about 20 mins later... the z2 was still drying

 

Wash the car and apply a layer of Z2 right over the existing one .. it will disolve it then when dry.. buff it off .. or wash .. buff off whats left and apply another layer ..

Just don't try to buff it off without washing.

As with any sealant it likes to have 24 hours after its removed to cure properly. This inclusdes no water.