Microsoft released the Exchange 2010 SP3 Update Rollup 18 on 6 July 2017.
I installed Update Rollup 18 on my test SBS 2011 server this morning and it took 11 minutes 30 seconds from start to finish, so I wouldn’t expect it to take much longer than this in production.
Please test before installing into your production environment. Maybe even wait a few days or a week or two from the release date to make sure the QA is up to scratch on it.
For migrations to Exchange 2016, Exchange 2010 SP3 Update Rollup 11 is the minimum version that will be supported in a coexistance environment.