If you miss the offline progress screen, for example, by refreshing the browser before this screen shows up, you miss that progress, getting just the equivalent of the new "offline" period of time.
My overnight progress is gone (upgrades, money and angels of the current run, the rest of the angels were safe), and my Black Tuesday plaque disappeared as well
 "AdVenture Capitalist"){kind=icon}
 "Rise of Mythos"){kind=icon}