What real-time constraints does PX4 follow?

Hi, everyone.
I have very little knowledge of the px4 documentation, and I would like to know if px4 gives any requirements about how long a module must be executed. I think real-time software can only be real-time if it has time constraints, and I would like to know how px4 reflects its real-time nature? Is it mentioned in the documentation? If not where should I look?

I would be very appreciative if you could give me some help.