How long does it take to replace valve cover gasket?

About as long as it takes for you to scream your head straight off your body. (because it hurts so much)

Wow, that was useful. Was that "primal scream" therapy?

Seriously, you're never going to find the answer to this online. Too much money is being made on selling these manuals to mechanics, and just about ANY "free" online source will have committed copyright violation if they publish times that are anywhere near the ones in the "official" guides.

Your best bet? Ask a mechanic you trust for a quote. Your next-best bet? Ask an authorized dealer's service advisor. Nothing says you have to let them do the work!

If you're adventurous, spend the $15 on a service manual at your local auto parts store (or look it up in a copy at your local library), buy the parts and do it yourself - it's pretty straightforward, but requires great care and attention to detail. You MUST clean ALL old gasket material from contact surfaces; ensure you don't drop any crap into the valvetrain; and re-tighten the cover bolts in the correct pattern to the correct torque - otherwise, you'll be doing it (or more) again.