You walk up to the outdoor unit and listen. The fan turns, the compressor goes quiet, then starts again a short while later. That on-and-off pattern is worth writing down before you decide anything about the system.
A heat pump that runs in short bursts is cycling short. Some of that is normal in mild weather, when the load is light and the thermostat is satisfied quickly. What you are looking for is a pattern that repeats on the same kind of day and does not match the weather.
What to log
Keep a simple note for the next week or two. Write down the time the unit starts, the time it stops, the outdoor condition in plain words such as mild, cold, or wet, the thermostat setting, and whether the air at the nearest supply register feels as warm or as cool as it did before.
Do not write a diagnosis in the log. Write what you saw. A log that says the run ended before the room reached the setting is more useful to a technician than a guess about the cause.
What to check on the walk-through
Look at the air filter first. A clogged filter reduces airflow, and the system can trip its own safety limits and shut down early. Note the filter size and the date it was last changed in your house file.
Walk around the outdoor unit. Leaves, grass, and debris close to the cabinet can restrict airflow across the coil. Keep the clearance the installer left and do not pack anything against the sides.
Check the thermostat location. A thermostat that sits near a heat source, a sunny window, or a supply register can read the room wrong and call for short runs.
What to ask at the service visit
Ask the technician to read the control board's fault history, if the unit keeps one, and to tell you what it recorded for each shutdown. Ask whether the short cycle comes from a control setting, a sensor reading, or the load on the house. Ask for the answer in writing on the visit record.
Then ask what the unit's age means for the next decision. Compare the install year with the planning window on the Heat Pump page, and write down the planning date you are working toward.
Heat Pump: typical service life and when to plan gives you the planning frame. A short-cycle log does not change the install year. It gives you a dated record to plan from.