So my last brew, I attempted to chill 8 ounces of water from boil to about 95F so I could rehydrate my yeast with it.
I boiled the water the prior to starting my wort chiller working on the 5.5 gallons of wort and tossed it in the fridge to chill while the wort cooled via the chiller.
By the time my wort had hit 75F, the 8 ounces of water in my fridge was sitting at a happy 120F. It was worthless.
Based off that experiment I imagine you would be waiting at least overnight for your wort to chill to a pitchable temperature. Immersion chillers are cheap and effective... I would recommend that over letting it sit in a fridge where it could potentially catch an infection.
