Staging without a proper thermostat is by the air handler's control board based on run-time ... the 2nd stage triggers after the 1st stage has run x-minutes, whether or not it's really needed. Perhaps call the installer to change the thermostat to a proper one?.
My thermostat is a Honeywell TH8321WF1001. It has choices (separate for cool and heat) for 2nd stage switching differential of "comfort" (controlled by thermostat algorithms presumably monitoring both time and temp swing) or by specific temperature swing of 1°F to 3.5°F from the setpoint in 0.5°F increments. Also separate for auxiliary heat droop, comfort, or 2°F to 15°F in 0.5°F increments ... OR time-based of 30, 45, 60, 75, 90 mins, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16 hrs AFTER 2nd-stage compressor.