The effects from oral consumption of cannabis can last 4-6 hours or longer depending on how much is eaten and how it was made.
I miss read, but that kind of relates anyways so i'll leave it. It you want a longer high eat .5-.75g in a firecracker or something.
Smoking for me the high usually lasts an hour with some after effects up to a couple hours later.
I have heard eating will shorten the high. Drinking a lot of water however may potentiate it.