If you are sure that the one switch controls both hob and oven, it is possible that the wiring in the switch is loose.
You should only check this with the power turned off at the fusebox.
If that checks OK, the next thing to look at is the connection in the oven. This will mean removing the oven from its housing and checking the electrical connections at the back, where the cable enters.
If this checks out as OK, it would probably be the clock mechanism itself at fault, as the whole oven is supplied through the clock.
If yu need more help, please just ask.
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