Catnip give the high or euphoric affect to cats for ten to fifteen minutes. It isn't long lasting at all but cats love it and it is often used as an attractant in cat toys to get them to play with them.
1 Additional Answer
The effects of catnip will only last about 20-30 minutes. Your cat will really enjoy catnip, but it affects different cats differently. It will either relax them, or it will make them hyper.