I’m not sure it really worked, actually. I changed it (back in 2015, according to our Admin log) on the Rails console using
Back then, there was no validation of that input. But it seems there is now, and the input of anything that is not in the enum results in
from /var/www/discourse/lib/site_settings/type_supervisor.rb:207:in `validate_value'
That’s probably a good thing in terms of Discourse code quality and stability. But I do get the OP’s point about wanting better options here. The 30 and 60 minutes options seem odd.