I'm not sure what the conflicting information from the friends would prove except that they have imperfect memory. But the timeline is what it is. Table booked at 8:30. Report to police at 10:10. They had just over 90 minutes to notice that Madeleine had OD'd, figure out how to hide her somewhere so that nobody would notice the body, or them walking anywhere but between the room and the table, and then coordinate their stories and report it to the police. And that assumes that the McCann's would be able to convince four other people who would have nothing to gain, and everything to lose, to participate in a conspiracy after the fact.