want an easy to memorize good enough ballpark for how much downtime per year "nines" of uptime give you? start from 100 hours for 99%, and divide by 10 with each 9 you want to add.
99%? around 100 hours (actually 87h40m)
99.9%? around 10 hours (8h45m)
99.99%? around 1 hour (52m)
99.999%? around 1/10th of an hour → around 360s (5m16s)
99.9999%? going by the rule would be 36s (actually 32s).