Why does adding an IF statement alter the outcome of the calculation occasionally?

I am trying to calculate overtime, and am using the following simple setup (file attached):

A1: 07:30
B1: 15:15

C1: =((B1-A1)*1440)-465 This will show a positive value if the difference between A1 & B1 is more than 465 minutes, and a negative value if it's below 465. I get 0, which is correct
C2: =IF(A2,((B2-A2)*1440)-465,"") Should give the same outcome, as long as A2 is not empty. I get -0.00000000000005684342 ...


However, if I repeat the same process with 08:30-16:15, both formulas give me the correct answer, 0

Why is this happening?