Disable time end time based on start time from drop down lis

Question

Hi,

 

I want to disable end time based on start time selection. i am using listitem in grid

 

eg: Suppose I select 12:00 from start time dropdown list.   

      Now  in end time before 12:00 all the time should be disable.

 

how to achieve this through c# ?

Pls help.....