I am autoclaving media to use later to inoculate yeast. How much time do I have to wait before using the media and adding the culture? Can I use it a few hours after autoclaving?
There is a relatively simple (and yet logical) answer: You can use the media as soon as they are cold enough for your desired culture temperature. So if you want to use the media at 30°C, there is no need to wait longer. The media will only warm up again in the incubator until this temperature is reached.
The addition of antibiotics is also uncritical, since the media is ways to hot to be directly used when they still inactivate antibiotics. Your cells wouldn't survive this either.
There is also no waiting period necessary to use fresh media after autoclaving, since there are no processes going on when the autoclaving was done properly. If not, you will see contaminations pretty fast.
If not using antibiotics or other additives, it's just a matter of medium being cold enough. If it's too hot, the yeast (or whatever you are inoculating) might get killed or heat-shocked, which you maybe don't want.
Since the incubator will bring the culture to 30C anyway, there's no point cooling it past that point. Yeast are probably fine at 37C, maybe even 42C depending on what experiment you are running.
If you put the hot medium into your culture vessel first then wait, it will cool faster, since the glass won't be as hot. When I feel impatient I like to run cold water down the outside of the flask while swirling, cools it off very fast.