Two aircraft heading towards each other in each pilots one o'clock. Not quite likely to collide but too close for comfort.
But if one plane is coming from the continent, and the other from the UK. There is an hour time difference. If they are doing traffic avoidance on local time, this could affect safety, as one might actually be at 12 O'clock!
What about daylight savings time? This could also make the right of way for "O'Clocks" more complicated....