Can you take the contraceptive pills earlier on some days?

It depends on what pill you are using, if you are on a "mini-pill" of only progesterone you need to take it every 24 hours give or take 1.5 hours on either side. Taking a mini-pill even 3 hours late is the same as missing a pill.

Taking most BCP, a combination of estrogen and progesterone - as long as you take it every day - you are protected from pregnancy.