Isn't Izzy in Belgium right now? Maybe she can even meet the creator of Go4orienteering, Luc Cloostermans. https://www.go4orienteering.org/?lang=en
In terms of minimum sessions time I also do not set a minimum, but struggle with sessions shorter than 45 minutes when kids are younger than about 7-8. In classes where teachers have the students under control, and kids are good about following instructions, and teachers readily pitch in with handing out pCards, maps, etc., 30-45 min is doable with 4-6 y olds. It gets tough when you are told you have 45 minutes, but they come to the session and it takes 10 minutes to get started. And even if you supposedly had time until 11:50, you are told 11:30 it is better to finish at 11:40 to allow time for the kids to gather up, wrap up and give kids extra 5 min before washing hands. Suddenly you have a 25 min session.