Time estimates for fixfdmn

This may be an unanswerable question, but I am curious!

We had a filesystem glitch on our SAN last night causing an advfs
domain panic (RAID unit went offline, not from a disk failure, more
likely a firmware hangup; and one domain had corrupt SMB metadata
after restart).

So I am sitting watching our ES40 run fixfdmn and wondering exactly how
long I might expect it to run, for a 1TB filesystem, about 25% used.
So far we're only a little over 2 hours. Wonder if anyone has experience
with this - even an "order of magnitude" idea would be interesting!

Graham