it sounds like your car is set to 'time and distance' rather than long life. Ive had the exact same dash warning ... with no warning! on saturday. rang the dealers and they told me its cos the car was set to 't&d' rather than longlife at the pdi. car is now just 12 months old hence the warning.
I think that you only get the 'countdown' based on mileage and not on time, hence at 364 days you are ok, at 365 its 'service now' regardless of mileage
regards
Mark.