[julie_m]

We can infer from the position of the relay that L and F most probably are connected to it; remember these are heavy-current traces, probably 2mm. wide and with 2mm. spacing, so they won't be going all round the houses.

If the data sheet linked upthread is right, T will be the switched live from the light switch, L will be a steady live and F will be the switched live to the fan.

It's probably using an electrolytic capacitor which charges from T and discharges via the pot for the timing; the voltage will be fed to the base of a Darlington pair (so most of the stored energy goes via the discharge resistor, as opposed to the base) switching the relay. At any rate, it should not require massive effort to reverse-engineer. If you take a photo of the solder side, flip it and print it, you can draw the components on it as though it were an "X-ray view" of the copper traces. Then it will be easy enough to draw out the schematic.