In peak season if you have the flexibility we find it better to travel very early or later on in the day outside of the main traffic. On a decent run it take us 3 hrs 15 mins from Junction 17 of the M4.

If you head off early park in the main Marazion carpark on the beach and have a day there before coming to the apartment. Or stop off somewhere on the way down once the majority of the journey is done.