Just the conversion process of transferring your pages over to the new system depends on the size of your site and the number of files stored in the lockers. Small sites will convert in under 5 minute whereas large sites with hundreds of pages and thousands of files can take several hours to convert.
The time required to fully switch your site over from the old system to the new, including template setup, conversion, build homepage content, clean up interior pages, etc., also depends on the size of your site. A small school site could take 1 to 3 hours of work. An average size middle or high school site could take 4 to 10 hours. A large district site could be 15 or more hours.