Is it strange for my two male cats to disappear at the same time??

Is this normal? Yesterday morning I noticed that they had both gone. The last time I saw them was after midnight. They are indoor outdoor cats but they only ever go out for a hour or so and hardly ever together this is very very strange. One is 6months old and not desexed and the other is 1year old and desexed they are both ginger males. This is in the Whangarei area