I was just wondering if there are any laws on getting days off, for example is it legal to only get one day off in a month, in a full time (40+ hour per week), non salary job.
Thanks in advance

There are no Federal laws and no laws in Oklahoma (or in most states) addressing days off. You could conceivably be required to work 365 days a year and with rare industry-specific exceptions it would be legal.

A very few states have a law requiring one day off in every seven but Oklahoma is not one of them, and even the states that do often have multiple exceptions.