We have an uptime guarantee of 99.8% and we try to remediate any downtime within 1 minute.
BTW, with the 99.8% uptime, we can be down for 30 mins, every month (which itself gives us 99.9%). I am not saying, App will be down for such a long time, but its our permissible downtime, as per our contract
But rest assured,we have 24X7, Premium support with Amazon, and they have been helpful enough to ensure we maintain our SLA, for the past 1 year (Knockwood)