I live in rented accomodation. The landlord is a pain in the asss, I never use the oven so I have no problem using it as part of my chemistry set. The oven is a cheapo calor gas, piece of. The thermostat (HA!) is a twist knob with no markings. I look at the flame, it is either high or low, so I use low. I also open the patio door as there is no vent for it. I've been caught out by CO poisoning before.
Regarding plaster, as far as I know and googled, there is only water comming out of the plaster, the chemical reaction has already finished. Even during the chemical reaction, it was harmless, except for the heat.
I judge the time by picking it up every 30 mins. If it feels light, it's done. Usually works out about 90 mins.
I find that if you over do it, the mould can get powdery and be a problem sealing if you use a brush. The brush disturbs the surface. If you are not sure and want to use a brush, use a very soft brush, landlords cat works well. Turn it over on its back and test it (the mould, not the cat). If it does wear the surface, use a different method, I splash a 50/50% PVA (elmers) water mix, without touching the surfaces and leave for 24 hours.
Sorry, got carried away there!