A few hours of Perl a day for 6 months should leave you with the ability to code properly and find the modules you need for most tasks. You'll do fine as a general-purposes programmer who has to design solutions on the fly for a variety of problems. However, it will probably take you significantly more time to really know Perl, to the extent where you can actually understand and modify the code inside the modules you're using. How much time? This depends entirely on how dedicated and intelligent you are. A general-purposes programmer won't have the time to study Perl to that depth, and some people simply may not have the mental capacity for it.

Bottom line, it's pointless to try to quantify the amount of time necessary to make a good Perl programmer.