time from 2 files to compare

In first file say first.txt, i have a content say 14:56. In second file, say second.txt i have content say 16:01.... I want to compare if these two times in these 2 files are having a difference of 15 minutes...Can any one please help?

Are you asking about a line *IN* the contents of the file, or is this the TIME STAMP from when the files were created/modified/accessed?

I am talking about the strings inside the files...