First you have to
cast
the Time to
integer
format
var Time = '<%=Session["Time"]%>';
var timeInt = parseInt(Time);
To get Current Date value
var currentDate = new Date()
To Add Minutes
currentDate.setMinutes(currentDate.getMinutes() + YourValue )
To create a date from the drop down values use this
var d = new Date(year, month, day, hours, minutes, seconds, milliseconds);
make milliseconds and seconds as 0 rest you can get from the picker and ddls.
Compare dates
if( d2 > d1) alert ('something'); else alert ('something something');