This suggestion is seriously on the DIY side of things, but has quite a bit of practicality to it. The typical microwave oven with a turntable within will have a motor that operates at six revolutions per minute, ten seconds per rotation.
The requirement of 25 seconds means a 2.5 to 1 ratio. I have dismantled a few discarded ovens and found one type with a motor that operates on 20vac, and a different type that runs on 110vac / 60Hz. I do not know what one might find in European countries (50 Hz), but I suspect the RPM will be 5/6ths or 6/5ths of the USA versions. This means a different ratio to accomplish the objective.
The motors will likely have a D-shaped shaft end. It is relatively simple to use a product known as hand-moldable plastic to create an adaptor. This would allow the attachment of, for example, a twenty tooth gear or a twenty millimeter diameter pulley. The match for the twenty tooth gear would be a fifty tooth gear, providing the two point five ratio. The pulley would, of course, be fifty millimeters for the same reason.
On one point of the output "wheel," you could have a rigid "finger" to strike a semi-flexible surface, causing a click. You could have a stationary pin which would cause the finger to flex back a bit, then strike another surface, perhaps a bell as it continues to rotate.
If you have a 3D printer or know of a makerspace in your area, the manufactured objects and even the mounting assembly would be relatively easy to create or have created.
The motors are smaller than 7 cm and about half as deep, with mounting ears for easy attachment. Gears or pulleys can be 3D printed or cut from 3 mm plywood by hand, scroll saw, laser cutter and mounted with the relatively common skateboard bearing. Gears are meshed, pulleys would require a belt, which can be an off-the-shelf O-ring. All of this would fit easily within your constraints.
It will certainly have a home-made appearance, perhaps reducing "attractiveness" for theft.
Image below created by software licensed to me:
50 tooth to 20 tooth