Is expanding foam coming out of an electrical socket a hazard for tonight?

REPLACE the receptacle!

You might have rock wool.  Which is similar to pink fibreglass but cost less and is about as good.  I seen the hardboard (almost like rockboard is what I would call it) I guess termite proof.

.  The foam is safe and will expand for a few days. It goes on a long time like 4 times its volume.  Safe electrically and you got to use up the can in one day.  Otherwise it dries in the nozzle and tube and is junk as you can't get it out anymore.

Fluffy stuff? you have sheep wool.

If you want to be completely safe, turn off the power, remove the outlet and cap off the wires with wire nuts.  Then replace the outlet at your earliest convenience.  Make sure to make a diagram or take a photo of where the wires connect before removing them.

you're good.  that foam isn't an electrical conductor anyway

Expanding foam ? Insulation ? Havent seen it is it cavity wall ? studded wall then its inside ? Are you sound proofing ? Just curious 

It should be OK for tonight. The thing you need to investigate is if the cable serving the outlet has become buried in the insulation and is not loose within a conduit, then you are in breach of wiring codes. The risk is that wiring will overheat, short and either fail or cause a fire. Update - once did a job on Waiheke Island, so the construction sounds very familiar, a dollar to a cent there is no conduit.

It'll be fine When it dries Use a sharp razor blade to trim off the dried excess foam