You should take it easy when first using a steam room.
The maximum amount of time for a first session is usually 7 minutes at around 110F if the room was already pre-heated.
If stepping into a cold steam room, you can stay around 13 minutes since it will take about 5 minutes to get it warmed up (depending on your steam generator).
Make sure you consult your doctor before using any type of steam room. You should absolutely not use one if you have an existing heart condition.