Three nines, five nines, bunch of nines...
The only people who seriously deserve to discuss "five nines" uptime are people prepared to pay for massive redundancy required. Five nines is one hour downtime per DECADE. Some shitty line of business reporting app used a few hours a month does not require that level of availability. It shows cowardsly/lazy specifications when "two nines best efforts during core business hours" is what they really want to pay for.