While I’m sure there’s a mechanical solution, my preferred solution (in terms of implementation time) would be to simply buy two hourglasses—one that measures 25 minutes and one that measures 5 minutes—and alternate between them.
Or just bundle them together like this: https://www.amazon.de/Bredemeijer-B0011-Classic-Teatimer-Edelstahl/dp/B00SN5U5E0/
While I’m sure there’s a mechanical solution, my preferred solution (in terms of implementation time) would be to simply buy two hourglasses—one that measures 25 minutes and one that measures 5 minutes—and alternate between them.
Or just bundle them together like this: https://www.amazon.de/Bredemeijer-B0011-Classic-Teatimer-Edelstahl/dp/B00SN5U5E0/