The usual references for how object-oriented Perl works are perlobj, perlboot and perltoot. These describe the mechanics of constructing the appropriate modules and interacting with objects. Many people choose to use previously-rolled object-oriented frameworks in actually building their code. Examples of these include Moose and Mouse.

Can somebody give me an idea that, how much time/days it would take for me to become expert in OO Perl ?

The term "expert" gives me pause. I am certainly competent with Perl in general and OO Perl in particular, but I would by no means characterize myself as an "expert" after years of work and study. Your mileage may vary.

Also, i have confusion in what is OO perl ? Please what exactly this means ?

Object_oriented_programming is a programming paradigm, which is to say a philosophy of how to build code. Some languages, Java being first in my mind, are built around the idea. In Perl, on the other hand, it is simply an approach to designing one's code. At its simplest level, it just means using blessed objects to maintain context for method calls.