Water on drywall ceiling underneath toilet help

This morning the toilet overflowed and there was a pool of water on the bathroom floor. It was cleaned up with towels and the toilet was plunged and seems to be working well.

Several hours later several feet away from where the toilet is located one floor below there is now a wet spot on the drywall ceiling. It does not seem to be expanding. Our theory is that perhaps the water leaked down between the trim and the baseboard vent/heater and is now saturated through but we are unsure.

Does anybody have any opinions on whether this is likely to cause problems or whether we should monitor for the next 24 to 48 hours.

Might it cause mold in the future?

Any help would be appreciated.

It sounds like the water flowed over the sheetrock to a lower point.
I would poke a very small hole in the middle of the wet spot on the sheetrock to drain any potential pooling water. If there is no fiberglass or similar insulation in the ceiling, it will dry out quickly enough and there will be no mold or further damage. If any water dripped out AND there is insulation, it is probably worth opening the ceiling in that area to dry it out.
After it is all dried out, prime the stains with Kilz primer to block the stains, and then paint it.

Everything fixitron said, but wait a month to prime and paint it.

Wet drywall can hold some water inside for a very long time.

If you paint it or try to spackle it or repair it with joint compound while even slightly damp, it will fail or get moldy or both.