It is impossible to estimate the time it would take you to become proficient in OO-Perl.

As you already know Perl it would mainly depend on how much background about OO-principles you bring from other languages.

I think a good starting point for you would be Damian Conways's book "Object oriented Perl".

It is a couple of years old, but it is still a good intoduction to (pre-Moose) OO-Perl.

Read that first and then take a look at Moose.