Minecraft wiki entry for Hourly_clock, associated text: To set this clock to the right delay, set 50 of the repeaters to 4 ticks, and 25 to 2 ticks (or 62 repeaters to 4 ticks and one to 2 ticks.) This creates 25 seconds delay and, with the inverter setup on the chime, will sound the signal once every 50 seconds.