Requested WoW macro

I want this macro to cast rejuvenation and my cat form which i know is /castsquence rejuvenation; cat form. but if rejuvenation is already active on me when i want it to just take me in and out of cat form if i click it again. like is there anyway to make the rejuvenation part to have a 12 second cool down? (how long rejuvenation last)