The laps on https://www.attackpoint.org/sessiondata.jsp?sessio...
are the markers.
Time trial starts from the lamppost just after the M50 bridge, so you guys started a bit early.
Split 1 (lap 2 marker on activity) is as you enter the forest.
Split 2 (lap 3...) is as you hit the bottom of the boneshaker and turn up the hill.
Split 3 (lap 4...) is as you finish the boneshaker.