We just released an update that puts some polish and much wanted new options on the Check stats & metrics page.
You can now use the date search box to select any date range you wish. Date ranges starting more than 30 days ago have a resolution of 1 hour.
You can use the forward and backward buttons to hop an hour in each direction.
The graph now shows clear markers on each failed check. Clicking the marker takes you to the failed check's detail page.
All uptime metrics are reported with Five Nines notation now.