Paying off the card before the introductory APR period is over will ensure that you won’t be stuck with a remaining balance at the end or have to pay interest. But, this will also mean a higher monthly payment than if you were to take the entire introductory period to pay off your balance.
Paying off your debt early is great if your budget can handle it, but so long as you pay enough monthly to pay down the balance before the offer ends, it's alright to take your time.