Hope it helps! The green icon on the status bar can display the current time on battery if you right click it and click timer.
For the record my 2011 11" i7 air lasts about 4 hours 30 minutes with light use and careful consideration for saving battery (50% brightness on lcd and keyboard, 50% volume, safari, mail, messages, and itunes open. No flash videos using the clicktoplugin in safari). It lasts about 3:30-3 hours if I use it without regard to saving battery.