I would normally quote 5 hours, but it can be done in less.

Alternatives to driving:

Flying
CraigAir http://www.craigair.com/

Luxury Private Shuttle
Pacific Rim Five Star Navigators http://www.pacificrimnavigators.ca/ -highly recommended

Bus/Van Shuttle
Tofino Bus http://www.tofinobus.com/ (2 daily departures)
Greyhound http://www.greyhound.ca/ (early morning departure; twice daily in summer)

Feel free to PM me if you have any further questions about the Tofino area.