I assume you're talking about hardy hibiscus. Deadheading doesn't really help much, but it can make for a nicer looking plant if you don't want seeds. The blooms are only going to last a day or two at the most, no matter what you do.

In past years, I've tried keeping some Hibiscus Syriacus (Rose of Sharon) deadheaded...just to keep it tidy. I soon discovered after they had gotten so big, and had so many blooms, that it took a lot more time to deadhead then what I had to give to the task.

Sue