Phil, 1300 is not an acceptible time format in Excel. It will see 1300 as an integer. Now, 13:00 is perfectly fine.

Now here's something you can do... if you're SET on having to input "1300" in a cell, you can use this function to convert it to proper time:

=LEFT(A1,2)&":"&RIGHT(A1,2)

Assuming your "1300" is in cell A1. Then, just format the cell as a TIME and you're good to go.