C# - Saving DateTime With WebMatrix And Razor?

I am developing a project that has a DateTime field.

In it I'm using jQuery for the user to select the date format 'dd/MM/yyyy' taking into account that the date is not a required field.

How do you do to save DateTime fields not required in WebMatrix and Razor?

I was trying to do something like this:

I put only the code which I think is important to complete the code can be found here

@{
//Get data
string TaskForecastCompletion= Request["txtForecastCompletion"];
string TaskCompletedIn= Request["txtCompletedIn"];
DateTime dtForecastCompletion = default(DateTime);

[Code]....