Time Validation script in pdf form

The best way to check is one time is greater than another is convert it to a date object, filling in the day, month, and Year with some arbitray value. 

Here's a script for 2 dates

// Get date string 
var strTime1 = this.getField("Time1");
var strTime2 = this.getField("Time2");

// Ensure they are both valid time strings, and convert to a date object
var rg24hrTime = /^\s*(\d{1,2})\:(\d{1,2})\s*/;
var oTime1 = null, oTime2 = null;
if(rg24hrTime.test(strTime1))
    oTime1 = new Date(2000,1,1,RegExp.$1,RegExp.$2);
if(rg24hrTime.test(strTime2))
    oTime2 = new Date(2000,1,1,RegExp.$1,RegExp.$2);

// Make sure both are valid times before testing
if((oTime1 != null) && (oTime2 != null)){
   //check direction of time difference 
   if(oTime1 > oTime2)
      app.alert("Time 2 must be less than Time 1");
}

But your problem is more complicated.   You need to check 4 dates. Before writing the code you need to figure out a couple things. For example, does the code check if one or more of the times is not filled in? What if they are filled in out of order? is this allowed?

And the really big question, how is the code going to decide if a time crosses midnight? or if it is earlier than the previous time? I would make the users enter the Date as well as time, so there is a explict indicater of the date for a specific time. 

Once you know these answers the code above can be employed to test the times.  

> Also how will this work then the times cross midnight. 

It won't. You need to either ask for the full date, not just the hour, or set a limit on the length of each section.