caluclate Time difference (value(endTime - StartTime))

Question

using ASP.Net MVC 4
caluclate Time difference value = endTime - StartTime
 without using model class i have two textboxes (Starttime and endtime) the DB of starttime datatype is nvarchar(50) and endtime datatype is nvarchar(50)
how to convert the Time format for caluclate the Time in mvc4
if you known please help me to solve....... 

using jquery this time value bind for hidden field value

regards,
manjula.D