It would help to know which OS you're using to give you an exact answer. In both Windows / *nix, you should be able to do this easily with output redirection and sorting from the command line. This is all assuming the timestamps are formatted the same way and each line is either blank or contains a timestamp.
Here's my 1 line windows example: type file1.txt > file3.txt & type file2.txt >> file3.txt & type file3.txt | sort | more