by Rick Jerz.
I agree with what Ken and Marcus have said.
There is a big difference going from 3.11 to Moodle 4.0 versus from Moodle 3.0 to Moodle 4.3.3+.
Your question appears to be hypothetical, and it appears to mix the administration of Moodle (i.e., upgrade) with the training needs of staff. So a hypothetical reply would be somewhere between 1 hour to 3 years, since I have no idea your Moodle administrator's skill nor your staff's ability to learn anything new.
A good place to start is to have your Moodle administrator try upgrading your Moodle 3.x to 4.x and see if it takes more than an hour. Also, have you tried setting up a course in Moodle 4.x and timed yourself?
There is a big difference going from 3.11 to Moodle 4.0 versus from Moodle 3.0 to Moodle 4.3.3+.
Your question appears to be hypothetical, and it appears to mix the administration of Moodle (i.e., upgrade) with the training needs of staff. So a hypothetical reply would be somewhere between 1 hour to 3 years, since I have no idea your Moodle administrator's skill nor your staff's ability to learn anything new.
A good place to start is to have your Moodle administrator try upgrading your Moodle 3.x to 4.x and see if it takes more than an hour. Also, have you tried setting up a course in Moodle 4.x and timed yourself?