You can set the “Availability Schedule Name” of your HVAC system to be the same as your occupancy “Number of People Schedule Name”. The HVAC system will be off when the availability schedule is zero and on when it is anything else. Of course, if there is an extended period with no occupancy and the floating temperature deviates significantly from set point, the HVAC system may not be able to recover within, say, a single timestep depending on the available heating/cooling capacity.