VBA Compare time/date in columns to select data for the same period only

I have an excel sheet with data in the format below, datetime (i.e. 20/01/2015 09:00) in 15 minute time steps in the lefthand column and measurement data in the right hand column. I am writing a code that takes this data from various .CSV files and pastes them into the same sheet in adjacent columns.

column (a)A123-P1a      (b)           (c) A123-P4       (d)       
20/01/2015 09:00    -9999.99    20/01/2015 09:15     -9999.99           
20/01/2015 09:15    0.0642      20/01/2015 09:30     -0.0668            

when the data is pasted it has different start and end times. I need to find a macro to check the start/end times of each column, choose a time period which includes all of the datasets and delete any times and data outside of this.

Can anyone help me with the code I will need?

Cheers

Sarah