In the figure we have a circuit where two 555 operating one as astable and the other as monostable allow very long timings to be reached, reaching 4 hours in the given version and more if additional counting blocks are added. In this circuit, the first 555 produces pulses with 30-minute intervals, which are applied to a frequency counter / divider N8281 or equivalent. Pulses with the desired timings obtained from the output of this counter / divider are applied to a monostable 555 thus providing the output command. In the diagram, instead of using two 555, we find a double 555 (556) with the corresponding pinouts. The output step will produce a pulse whose duration will depend on R and C. This pulse can be used to drive a power step with a relay or other device as a load.
