I am a FT employee. Worked 40.24 hrs one wk, then 37 hrs the next wk, all in the same pay period. My employer is now refusing to pay .24hr. Legal?

Generally, federal law requires an employer to pay overtime (for hourly and non-exempt employees) at the rate of time and one half  for all hours worked over 40 in a "work week."  The requirement doesn't depend on the pay period.  However, there are exceptions to the rule.  For instance, if you work for a company which has a union, the labor contract could allow you to work more than 40 hours per work week without receiving overtime in certain circumstances.  Also, if you are employed by what is called a "local enterprise" engaged in the wholesale or bulk distribution of petroleum products, you may not be entitled to overtime under the facts you describe.