I'm sure with proper calculations this can be achieved. Two words come to mind...Maintenance Window. How do I know my "switch version" process is not going to exceed my maintenance window? A timer won't prevent this but it would at least give me time to alert the proper authorities and decision makers.
I agree if there was just an estimated time of how long it could possibly be like if your database size is greater than or less than this size and such. Sort of like Chris said it really depends on factors I am doing a update this weekend and it would be nice to know around the time it would complete
just fyi, it ended taking roughly 45 minutes for the switch version to complete. now on to the CCX subscriber and have it switch version =/