startdate and endate validation in datetimepicker in c#

Question

Startdate datetimepicker1

Enddate datetimepicker2

i want to validate three conditions from the above startdate and enddate in datetimepicker.

Startdate always be monday's date

Endate always be saturday's date

startdate must be less than enddate. the date differnce is 12 days

if user select the start date 10 mar 2014 (monday) then end date must be 22 mar 2014 (saturday)

for that how can i validate in asp.net using c#.

REgards,

narasiman P.

please help me.