Need Countdown Timer in Excel with automatic reset to pre-determined value

I am looking to create individual 15 minute countdown timers in 20 different cells (e.g. A1 through A20) with a linked Macro which will start the countdown when clicked, and then, upon reaching "0", automatically reset to 15 minutes and stay until the clicked again. This is what I have come up with so far that's working but it won't reset.

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I specifically need it to "start" counting down when I click the cell and reset to 15' (but stay until clicked again)

Please help. I feel as though I am close but have been trying to figure this out all day.

Also, I can't figure out how to create a "Normal Module," a "Workbook Module," or a "Sheet Module." Please advise. Thanks so much in advance.
Steve