Return Time Intervals Based On X Minutes

I have a spreadsheet set up that has a series of timestamps and values. Please find a copy attached. I need to set up a macro that will allocate the timestamp in column C to an interval of time, e.g between 12:30 - 13:00.

To achieve this I tried to set the following code up in VBA, which would input a letter in a blank cell based on the time interval that the timestampin column C falls into, for example if the timestamp is > 12:30 and < 13:00 then "A"...the plan was to extend this concept to accomodate all of possible the time intervals I have.

Sub time_intervals()

Dim x As Integer
Dim lastrow As Long
Dim timeA As Date
Dim timeB As Date
Dim timeC As Date
Dim timeD As Date
Dim timeE As Date

The idea was that the timemaster value would be the timestamp in column C of my spreadsheet and the timeA,timeB,timeC etc would reference the timeintervals. However this does not seem to work as the value returned by my if statement is always incorrect - for example timemaster in cell C2 is less than timeA but the if statement always returns FALSE as opposed to "A"