It's possible that the clock has been accidentally set to auto - i'e turn the oven on after a delay period.
Switch the oven off and on again so that the clock flashes then set the clock
Depress and hold in buttons 2&3 from the left and use the plus & minus buttons to set the clock - any time will do - the oven knows no better.
This is just a guess - I also guess that you don't know where the user manual has ended up.
Good Luck...
April 2016