18) B

This question is only asking about September.
Possible square numbers in the hours place: 01, 04, 09 and 16
Possible square numbers in the minutes place: 01, 04, 09, 16, 25, 36, 49
Possible square numbers in the day place: 01, 04, 09, 16, 25
Possible square numbers in the months place: 09
We need to find out how many different digits there are in the numbers above. There are:
01, 04, 09, 16, 25, 36 and 49. So there are 6 different numbers. We just need to square 6 to find the answer. 6^2 = 36. Hence, B is the answer. 
Alternatively, you can find the different possibilities but it will take too much time. 

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