In minecraft, how can I make a redstone repeater system that would activate "X" every 10 seconds?

Redstone repeaters can be set to delay the circuit either 0.1, 0.2, 0.3 or 04 seconds depending on how far the torches are apart (0.1 for touching, 0.4 for far apart). Using this you can generate a simple 10 second delay by chaining 25 repeaters set for a delay of 0.4 in a loop. It won't be compact, but it will be accurate.