The inside of my elbow hurts whenever I bench press/how many days should I take off?

It depends. Its either medial epicondylitis, a type of tendonitis involving the forearm flexors or else cubital tunnel syndrome, which is a pinched nerve on the inside of the elbow. Rest it for a week and apply ice 10-15 minutes 2-3 times a day and take an anti-inflammatory like Ibuprofen or naproxen. If it keeps hurting see a doctor for x-rays.