When a role is currently active, always allow future activations to be scheduled.
When my role is elevated the 'Activate' button is not always enabled to allow me to schedule a future activation of the current role, if needed. Sometimes the Activate button is enabled and other times it is not. I do not see a consistent pattern to determine why I can sometimes schedule future activations or not.
Currently, only seeing this for the SharePoint Service Administrator role (as that is the only role I used PIM for). I know this PIM is still in preview for this role, so may not be affecting other roles.