The 3-minute you're watching is probably the default permission for administrators (any administrator by default has 3-minute to all laboratories). But given that you're adding that permission to the group Administrators, and assuming that the user you're using is in the Administrators group, it should be reflected and override the default one, so you should see that. Can it be that you created a new user, of role administrator, but you didn't add it to the Administrators group where you are assigning the permission?
By the way, if you've started to develop labs few weeks ago, in the documentation was not yet listed the new library: https://docs.labsland.com/weblablib/
which makes the development easier.