Well, how long it takes really depends on which country you're from. You can either apply for your work permit at a CIC office in your country/region or you can apply directly at a Canadian airport of entry if you're from a TRV-exempt country. In case of the former, you could end up waiting for months and in the case of the latter, you can get your work permit at any time before your LMO expires. LMOs are valid for 6 months after they're approved. Here are the processing times for work permits from all CIC offices outside Canada:
http://www.cic.gc.ca/english/information/times/temp/workers.asp
Also, how long did it take for your employer to get an LMO?