In digital advertising, Dayparting is often associated with running pay-per-click ads at specific times of the day, with the goal of achieving the most impressions. With that in mind, when it comes to mobile advertising, knowing average daily impressions by the hour (or time of day) is vital in achieving a good ROI.
Average daily impressions by the hour (source: Smartinsights)

As we can see in the image above, Phone usage peaks in ‘Prime’ time, and drops during daytime/business hours. Also, Phones show a little spike in the early morning. Tablet, on the other hand, is mostly used in evening and prime. Therefore, to get the best bang for the buck, you should avoid 9 am – 5 pm and schedule your ads between 7 am – 9 am and 6 pm – 9 pm.
Example
For example, if we own a Coffeehouse, we should focus most, if not all, of our advertising in ‘early morning’. However, if we are in the business of selling Apparel, Accessories, or Hotel Rooms then our best chance of success is between 6-8pm (when Tablet and Phone usage is at its highest).
Obviously, this is a general rule which may not apply to your specific target demographic and industry, but it is a good starting point when planning your mobile advertising.
Related: Different advertising compensation methods: CPC, CPA, CPM, CPL, and CPI