I am not sure there is a good way to answer that question. Cisco has made it clear that 5.x is not considered an "upgrade" in the usual sense, and with good reason. The basic operations have changed significantly. However, with that said, if you are only using it for a few devices, I would not expect it to take more than a couple of days to get the hang of it and build some basic rules. The more things you use it for, the more users and groups you have, and the more devices you have, all will increase deployment time.
Knowing my way around it pretty well, I would expect 3 days or so for myself to configure 5.x for wireless, VPN, Cisco device auth for ~50 devices in different groups, backups, and all of the usual backend components. It could be as quick as a day, and as long as a week if there are more complex components including downloadable ACLs, dot1x, etc.
Your best bet would be trying a demo of 5.x to get a feel for it. I think in downloads you can still download a trial image to install in a VM.
Cheers,
Eric
