This is the worst part about changing ROMs, IMO.
For what it's worth, I did "dirty flash" from 4.0 to 4.5 with no real issues that I've discovered yet, but always be sure to take a NANDROID backup just in case you have to go back!
For general tips on how to speed up the restore period after having to do a ROM install with a data wipe:
1. Check out Nova launcher (or Apex). It runs very smooth on the S3, has a lot of great configuration options over the standard TW launcher, and you can backup/restore your configurations to SD card, which is a huge time saver when loading new ROMs, and the #1 reason I run Nova over TW launcher.
*(When installing CR, you do have an option to load Nova instead of the TW launcher, however I don't recommend that unless you're sure of what you're doing. If you don't load the TW launcher by default when installing the ROM, you may lose additional features that you want. Simply install Nova over the TW launcher afterwards).
2. Titanium Backup. Use this to backup all USER apps. I recommend hitting the Play store and running any updates you need before making your backup. When restoring, I prefer to use the option to let Google backup and restore my account, so that most of my apps are automatically re-loaded when I first logon after a new ROM flash. I then use TiBU to restore any missing apps once Google Play store has finished installing. Unless absolutely necessary, restore apps only, do not restore data.
3. MyBackup. There are several apps you can use to do this, but I find MyBackup works pretty well for backup and restore of SMS/MMS messages, as well as personal dictionaries. Remember that contacts and calendar are automatically synced with Gmail, so don't bother with stuff like that unless you have a reason to.
This is how I do it. Between the time it takes Google Play to install my apps, the time to run restore on my missing apps, SMS and launcher settings, as well as little tweaks like signing into apps and setting notifications, etc...I can usually get through a ROM install in just under an hour.