Recently, it was identified that the data used to produce these reports is not current. In fact, the data can be up to four days old. This is less than ideal for admins that want to work with the most recent (and hopefully accurate) data so that Pages can be tuned to increase the size of their communities and encourage more engagement.
If you are a Page admin, Facebook currently displays a message acknowledging this delay and their attempts to improve the currency of the insights data:
Stay tuned for progress on this issue. In the meantime, examine the insights for your Pages (if you haven't already done so).