program a formula to count number of times event occur before a specific time.

Hello,
Not sure if this requires a formula. Column C is the answer and counts the number of times taxis arrive before the time in column B. For example, 3 means that 3 taxis arrived before 6:57.
So basically I am trying to count the number of times taxis arrive (see the sheet attached).
Again, I need to count the number of times it arrived before 6:57 (30 minutes from the starting time 6:27), which is C2.
However, column D is not in time format and while I could change column B to remove the colon, i dont think it can be compared to column D. In addition, I need to do this to multiple sheets and it would be inconvienent to add 30 minutes to 6:27 if it is not in time format (i think).
I know its not hard to do manually but I have to do this many many sheets and will probably make mistakes. Can anyone help write a function so I can get column C (final desired column)?

Thanks!!