Need help with crystal reports xi formula - convert time from military to regular time

I have two fields - that are both numeric - one or appointment start time and one for appointment end time. They are both stored in a numeric field in SQL Server.

What I need to do, in CR XI, is read the following and I have no idea how to create the formula:
1) read in the number - ex. 1315
2) convert it to a string to manipulate it
3) determine the length of the string - if the length is 3, then I only need to go after the first position of the string because it is a single digit - for example - 815 as opposed to 1730
4) if the first two bytes are greater than 12, I need to subtract 12 - in my case of 13, I need to convert to 1, something like 17 would be a 5
5) then I need to put the first two positions together then concatentate with ":" and then the last two positions -

So if my value is 1315 - I want it to read 1:15 PM

Could someone put together a snippet of code to show me how to do this.

It would be a huge help!!!

Thanks in advance.