According to https://urbanoutdoors.com/hiking-fra...new-hampshire/:
There’s a designated parking lot for the trail – the Old Bridle Path parking lot – that fills up quickly on weekends. If that lot is full when you arrive, there is additional overflow parking further north on Highway 93 that requires an extra 2 mile hike each way.

What does it mean "fills up quickly"?
How early should I arrive on Saturday in August to make sure I can park there?