Can Walmart fire me for not paying for overtime they don't pay for?

Overtime is time worked in excess of 40 hours in a single workweek.  An employer is required to designate a workweek. Most workweeks are Sunday through Saturday, but it could any other consecutive 7-day period.  To determine whether overtime has been worked, you have to look at a single workweek (not a two-week pay period) and see if the employee worked more than 40 hour in that workweek.  If so, the hours in excess of 40 must usually be paid at a rate of 1.5 times the employee's regular rate of pay. Overtime is not incurred just because single workday is longer than 8 hours.  So, for example, an employer could require an employee to work 10 hours/day Monday-Thursday and give the employee the remainder of the week off and no overtime would be incurred. So if your employer required you to work 8.5 hours on Monday, 8 hours on Tuesday, 9.5 hours on Wednesday and 8 hours on Thursday then told you to come in (or leave work) 2 hours early on Friday, no overtime would be incurred.  However the employer cannot accomplish this over a two-week period.  If an employee worked 45 hours in one workweek, the employer cannot give him 5 hours off the next week and avoid the overtime pay obligation. I recognize the unfairness of the employer waiting until you show up the next day and then telling you to clock in 30 minutes late because you worked 30 minutes over your regular shift the day before.  I know of no action you can take to correct this, other than finding a new employer.