With the code I have now it output's the alert even if the format is correct. It's probably something really obvious but I have been at it a while now so I'm hoping someone can make me look really stupid 

Heres the code:

2. In_String = input.Custom_Time; //Gives variable "In_String" the value of Custom_Time inputted by user
3. Number = "1234567890"; //Defines variable "Number" to hold number values
4. Retval = false; //Creates value "Retval" to false
5. 
   
6. if ((input.In_String).length() == (input.Custom_Time).length())
7. {
8.     First_In_String = (input.In_String).subString(0,1);//Variable to hold the hours inputted by user
9.     Sec_In_String = (input.In_String).subString(2);//Variable to hold ":" symbol inputted by user
10.     Third_In_String = (input.In_String).subString(3,4);//Variable to hold the minutes inputted by user
11.     
12.     if (First_In_String == (Number))
13.     {
14.         Retval = true;
15.     }
16.     else if (Sec_In_String == (":"))
17.     {
18.         Retval = true;
19.     }
20.     else if (Third_In_String == (Number))
21.     {
22.         Retval = true;
23.     }
24.     else
25.     {
26.         Retval = false;
27.     }
28. }
29. if (Retval == false)
30. {
31.     alert "You must enter a time in 24 hour format, eg; 13:30 for 1.30 pm";
32. }