Stop Excel interpreting integers in a time-format cell as days?

[TomGoodfellow]

A particular time keeping system uses time cells (formatted as [h]:mm" ") to record events (start, stop, etc) as times of day. With a colon an entry gets interpreted as HH:MM even in the absence of minutes, e.g. "10:" becomes "10:00", but without the colon it is treated as days, e.g. "10" becomes "240:00"

How can I force a simple integer input to be interpreted as an hour? (preferably without resorting to macros, since the owner of the XLS will be change-averse)

[#2]

@TomGoodfellow 

This is how Excel works. It needs a : to interpret the value entered as time. If you enter a plain number in a cell formatted as time, it converts that number to days, since time is stored in Excel as a fraction of 1 day = 24 hours. There is no way to avoid that without VBA.

[#3]

I was hoping that some ingenious validation rule could fix the string rather just rejecting, but I didn't find any example of updating the value that didn't involve VBA.