Step 3: interface the timer to the LED driver
Next, interface your 555 timer circuit to the Buck Puck LED driver. This is easy. Just put a jumper wire from pin 3 of the 555 to the control pin of the Buck Puck.
I would wait to attach the Luxeon V to the driver yet. If you power it up, and it's not heatsinked, it can go into thermal runaway and melt itself down.
Note that the ref pin is not used.