There is no good time to break up, you know when the time has come so best to get it out of the way. It allows you both time to move on, plus around Christmas/New Year is probably the easiest time to get women because the single ones are doing the whole "forever alone" drill. Happy days.
I currently date no one, change of career makes it awkward to date for the first year or so, especially with civvies, so I cut off all attachments. It can be poop at times, but heyho.