There's an easier way than creating a second range. The third Friday for any given month will have a Day value of 15 through 21. Not only that, any Friday with a Day value of < 15 or > 21 will be a first, second, fourth, or fifth Friday of a month. Therefore, you can check to see if a date is a 3rd Friday with...
=IF(WEEKDAY(A1)=6,AND(DAY(A1)>14,DAY(A1)<22))
(...assuming the date you're checking is in cell A1, of course.)