Why do we recommend 7mins online Interviews (5mins walk, 2mins transition)?

The 2 minute transition is more critical for in-person events. Back to back 5 minute interviews could be a complete disaster when scheduled by Tes. It's bad when scheduled by humans, but the extra gaps due to inefficient human scheduling are essentially causing 5 minute or more gaps to 'walk'. When scheduled more efficiently by amazing Tes algorithms, there is vastly more back-to-back interviews than would ever occur when scheduled manually. So parents have no time to catch their breath, go to the toilet, or walk to and find the next interview. So while some level of back-to-back with 5 minute slots can work, it's the vastly increased volume when scheduled more efficiently that is the problem. So 7 minutes means a great balance. Users don't need to designate 2 minute walking time, you just keep slots at 7 minutes, and this naturally builds in the walk time. Note also that there is a snowball effect with a high volume of back-to-back short 5 minute slots, as quickly the event goes completely haywire, with no buffer time to restore on-time running.

Regards online events, the need to transition may be less, but it is recommended to go with 7 minute slots, though 6 could be an option. There is no walking, but parents still need some time between slots, if there are too many in a row. With 7 minute slots, it's easy for parents to have  all their interviews in a row, because there is time allocated within the 7 minutes for transition. But all interviews back to back in 5 minute slots would be difficult. So we could limit the maximum in a row, but this is not the right approach. Parents do not want a whole interview slot gap between each, as it doubles the time needed to attend the event, and makes the event less likely to run on time. Parents with a full free gap next are incentivised to keep talking longer, as they have no following interview. This causes problems, even though it seems valid and helpful to 'give' parents these gaps, or allow them to naturally have gaps using full manual scheduling, but this is just counter intuitive.

 7 minute slots means more efficiency with a small amount of time to accommodate some occasional longer talks needed, but more so to aid transition, and act as a buffer to ensure on-time running.

Summary:
After managing many events and engaging directly with schools:
5 minute slots manually scheduled is not good but 5 minute slots auto-scheduled is much worse, with more back-to-back interviews, and countering this with 'enforced gaps' or limits on sequential interviews is definitely not the best approach. It just serves to extend the event duration for parents. It also discourages subsequent attendance at events. Parents with tight back-to-back 7 minute slots, where they have a far reduced total time for all interviews, and less wasted time are more likely to attend future events.
7 minute slots offer a perfect balance in our experience, for both face to face and online events but possibly 6 minutes may be acceptable for online events, as parents don't need to 'walk' between interviews.