Off-the-shelf product, flash a light, change its tempo?

I use these things all the time and it will do what you want it to do.

https://www.ebay.com/itm/USA-1-PC-1...h=item3cd9e8c554:g:TCMAAOSw7NNT8Axt:rk:2:pf:0

Its not totally 100 percent plug and play, but a little bit of wiring will get you what you want. It has the ability to have an infinite amount of repeated cycles. For your case, the on cycle would be around .05 seconds followed by a .50 second off cycle.

It would help to understand what you are trying to accomplish. If you are trying to match an audio beat to the light (as a heart beat sound flashing the light as well), I have made that circuit before. I used it back in the day when I dj'ed to get lights to flash to the beat of the bass. It was a line level audio signal going to a voltage regulator, then to an opto-islator, then to a triac (a few other components were involved but the items listed were the nuts and bolts of the circuit). You could use the KA2284 and replace the LED with an opto-isolator then to a triac. Here is a circuit someone else made but its a little involved.

https://www.instructables.com/id/LED-light-vs-music-BEATS/

Okay, I had something completely else in mind, yea that timer would be a bear to keep changing. Okay, here are a few other ideas.

1. Using a laptop, download a program (Powerpoint may work for this) have a bright color flash on the computer screen for the BPM you need. You could create several different power points each assigned with a specific BPM. You could even connect a separate monitor for a larger screen for the chorus to hear.

2. If you rather have a light, using a laptop with an arduino board, you could create BPM sequences to flash a light through the arduino board.

3. There are several midi devices (aka a keyboard) that you can connect to a DMX controller for relativity cheap.

4. This one is old school. I have connected a 12 volt light to an audio amplifier before. If your metronome has an audio output (or keyboard that can produce a beat) connect it to an audio amplifier and adjust the volume until the light starts flashing. You will need to connect a dummy load (usually resistors) to match the impedance of the amplifier so you don't blow the channel out.

If any of these sound feasible, let me know and I can expand on the details.