I set the hook instantly, or very close to that, with most soft plastics. Some of the larger ones (senkos, worms, etc) I may wait a second or two. Literally. Not this 3-5 seconds I've heard people mention. Thats way more time than needed, and can result in missed or gut-hook fish.
As soon as I feel a bump, I drop the rod tip, and pick up slack until I can feel there is something still there. Then I let er rip. Total elapsed time from bump to set is usually a second or less. Sometimes you have to do a little more feeling around for the fish, but not five seconds.
Gut hooked fish needn't be common with soft plastics. Pay closer attention.