Begin at the building exit
Time the parking gate, the first traffic lights and the first busy junction. A map estimate that starts on the main road can miss the slowest part of the trip.
Repeat the journey in both directions if your schedule allows. The route home can feel very different from the morning departure.
Include the walking part
If the metro matters, walk from the front door to the platform entrance. Notice crossings, shade and the final distance at the other end of your trip.
The useful measure is door-to-door time on a normal weekday, not the straight line between two pins.