In a reply to enquiry mail, Google has answered that AdSense reports are usually updated every 15-30 minutes, with occasionally the full reports updating may takes a longer delay.
So, no need to worry about AdSense reports not updating, because even if you notice a delay in your account reporting, the stats are still being tracked and you’ll be paid for all valid clicks and impressions. Beside, it’s also normal if the statistics from overview reports is different from advance reports, because of the delays.
However, the delays do caused that it’s impossible to know or track revenue and value of each click. It’s simply not possible to know the increase of earnings is due to which clicks, as the increase will not be noticed immediately as it suppose to happen.