I'm sure Quinn means isobutane, not propane. I don't think anyone makes a propane canister that will fit on a Pocket Rocket. I think 40 minutes is probably excessive. I might have run my canister stove that much in winter, but that included melting snow for water and I wasn't running it full blast either.

I'd figure one canister for two days is a safe bet. If you wind up carrying an extra. you may run into someone who needs one.

This site has probably more stove info than most people will ever need, or want.
http://zenstoves.net/StoveChoices.htm