How long should it take to enable FileVault 2 on a fresh Lion installation?
Solution 1:
You might find that the time taken relates to the size of the volume to be converted (not limited to the amount used).
Personal estimates of duration may be difficult.
Expect the most reliable estimates to be offered by System Preferences. If the system was only recently started, don't expect an accurate estimate of time; and don't be surprised if the estimate rises occasionally.
For more detail than is given by the progress bar in System Preferences: in Terminal you can run the following command, which will display a tree view of the CoreStorage world:
diskutil coreStorage list
Within the tree you'll see sizes; amounts converted.
If a volume is heavily used during conversion, it might slightly extend the time taken to complete but for your 10 GB used I would not expect there to be any difference. Use the volume as you normally would until conversion completes.
Solution 2:
2 consecutive vault activations on a 2 new MBP w 750gb drives. Each was a clean Lion install with nothing else on it.
Time to encrypt: 12 hours minimum each time. By far the longest running disk encryption on any platform I have ever used. Also, this is the only disk encryption I have used that allowed me to use the machine whilst it was grinding bits. I accept the trade-off.
Solution 3:
Your mileage may vary, but it took about an hour to do on my clean Lion install (less than 10GB IIRC), Vertex 2 SSD. It'll obviously take longer the more data you have and the slower your drive.
Solution 4:
Mine may be the "untypical" case. Upgraded my mid 2010 2.66 GHz i7 MBP 17" from Snow Leopard 10.6.8 (including the supplementary update) to Lion, then enabled File Vault on the 500GB internal HDD (14+GB free) and continued working. Took more than 16 hours -- continuous -- as I didn't turn off the MBP until it was done.