That's not true. 5 nines, ie 99.999% uptime means that the maximum downtime in a year is about 315 seconds:

60x60x24x365 x (1 - (99.999/100)) = 315.36

Wikipedia confirms: https://en.wikipedia.org/wiki/High_availability#Percentage_c...

So yes, 2hrs of downtime would most definitely violate the SLA. The 8 hours you refer to is the figure for 3 nines.