Hi, Bob
When you say you write it "in a mail," do you mean a webmail interface? Or a desktop client of some sort? And does the change of (0) to "unwanted clockface" occur
as you're typing or after you type "3" and hit 'space'?
In general, it's likely that whatever program you're using (if it's not a webmail) has some auto-correct feature that changes the (0) to what you're seeing. If so, you can check the settings/options of your program to see if you can delete this particular abbreviation so that it doesn't auto-correct.
You can also try typing the number and whenever you notice the change occur, stop and type "Ctrl + Z." That should undo the change and revert it to what you originally typed.
Let us know.