I'd imagine they could see them looking at a phone and delivering the text at the time since they saw them on the bridge and turning onto the path.And yet they were caught at the exact same time frame the text was sent on CCTV down by the river bank with no other persons identified…
If the 2pm visit there was them getting the wrong time for an elaborate plan and had rucksacks with them containing stuff to take away with them, why didn't they take the rucksacks with them for the "correct" meeting time of 2am?
For such a good, clever and elaborate disappearance act, how could they have got the timing so wrong for the 2pm escape attempt?