If it's a bailey unicorn then you should have the alde heating system in. Which in that case has a timer function built in that you access from the control panel.
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You need one of these [link]
Fitted as standard by Buccaneer, wouldn’t know about other manufacturers.
There is also a free app available from Alde [link] but you require a control unit.
It would appear that the links that I tried to include in the previous post failed! Not a lot of use to you so I'll try again.
Truma Text Control [link" target="_blank">