Susan,

Why did you insert an extra column (F) and these two steps
1.Enter the specific interval, in minutes, in F2. In this case, enter 15 to represent the quarter-hour interval.
2.In G2, enter the following formula
=TIME(HOUR(E2),MROUND(MINUTE(E2),$F$2),0)

When you could have simply put the value 15 into the formula like this?
=TIME(HOUR(E2),MROUND(MINUTE(E2),15),0)