RoboCopy question

I am preparing to retire/replace a NAS on our corporate LAN. Total data is approx 600GB, much of which is static data but there are quite a few documents, spreadsheets, and other documents scattered about in users folders. I've used RoboCopy to copy the majority of our data to the new NAS (with permisssions, etc..). However I'm not sure which switches to use on the command line for the "final" copy, which will move all of the documents/files that have changed since the bulk move. I want to copy only the new/modified files, based on size and timestamp. I've read that RoboCopy can accomplish this, but the descriptions on the command line switches were not clear enough for me. Should I just run the Mirror switch or something else? If possible, please provide an example.

Thanks in advance,