The total downtime was 3 days for the production environment. We spent have a day upgrading the server, php, search for solution due to missing information in the documentation (some extension that are required are not mentioned), MySQL version upgrade and conversion... The upgrade of the Totara itself was easier because our partner had upgraded the repository before. Then it took us have a day to update the theme (attention - you may need to rebuild if you base your current theme on customtotararesponsive; we had done this before what tooks at least nearly a week), another day for HR Import changes (the file is called jobassigments.csv - you may find two different names in the documentation), implementing customized settings, reinstalling third party plugins, adopting SAML, and all this customized stuff; and another day for testing.

We created a nice funny maintenance page for the downtime that took learners to another place in the Intranet where we stored interesting videos and learning resources ... That limited the bad feelings of loosing time to learn things.