Like the other guy said 4-5 years. And that I would say I'm above
intermediate level but not an advanced level. I don't look at it
so much as how long to master OpenBSD but how long to master Unix!
I read somewhere when I first started learning Unix, that no knows
everything there is to know about Unix. So I'd say I'll be
spending the rest of my life learning Unix. I found that OpenBSD
is better to learn Unix than Linux. Linux I find to be to
overwhelming to learn Unix because of all the bloat it has (i.e. 5
text editors on one distro). I've also found that OpenBSD is hard
to learn to easy to use. It may be hard to learn what
configuration you need to change in a text file to make something
work the way you want, but once you learn, the task is as easy as
"making a change in a text file". I'd say subjectively that 80% of
"learning OpenBSD" is not learning OpenBSD, but learning bind,
sendmail, ftp, vi, etc. There are whole books on those individual
programs.