Don't you get that they were all "in on it" Sherlock? , <rolls eyes>
They did the sensible thing and tried to work out times, pinning them down to aid the Officers. Personally I would have been more suspicious if they had all matched and fitted perfectly.
I don't believe personally there was anything to be 'in on', but I do agree with you that it would be more suspicious for their statements to have matched.
Their timeline and personal statements have been analysed by many, including Heriberto Janosch on his website and on this forum, and the prevailing view seems to be that the discrepancies which exist in their accounts of events that night fall well within what would be expected in the circumstances: different people; on vacation not looking at their watches; distracted by their conversations and interactions with others; having consumed a certain amount of alcohol; going through fresh trauma on the night and still undergoing trauma of another kind whilst recounting events at a later date.
If they had decided to cook up a story, it would have been better put together, with as few ifs and buts as possible. Instead we have many 'flaws' - Gerry and Jez claiming not to have seen Jane Tanner when she witnessed 'bundleman' being one of them. If Gerry had asked Jane to collude in an account in order to protect him, he would not have denied her presence in witnessing an 'abductor'.