Yeah I just changed the old two categories to have old school in the name. I think probably the best timings now would probably be:

Start - when the doors to the portal start opening

End - when the last puzzle solve sound plays

I think any other end timing is a bit more fuzzy, because loading back into the hub is slightly computer/internet dependant - and then some levels in the full game have things out of your control that can change how long it takes to get to the portal, but don't effect the last puzzle(s). So this way would make it more consistent with how I'd imagine it will work in the full game. If you can think of a better way though let me know - I'll just throw that up as the rules for now so it's still possible to do runs.