The study was conducted by San Francisco-based mobile app optimisation start-up Sensor Tower, which offers an app analytics service that helps developers better understand how to improve their apps' keywords in order to increase their app's visibility in app store searches.

The company said it regularly fielded questions from its customers about the timing of new app releases, which actually vary a bit from category to category, and wanted to offer a more comprehensive answer to these questions.

The firm broke down downloads and revenue estimates by day for all iOS apps in the US in order to see what percentage of the weekly total took place each day, indicating the best time to launch or run a campaign.

The data is more relevant to those looking to promote their new applications by running campaigns to attract new users or purchases -- something that generally occurs alongside an app's launch, too.

The company found that the best day to run promos vary across the app store's different categories.

While weekends are often best as a rule of thumb, it seems, there can be some variance when it comes to when to promote purchases versus downloads.

For example, business apps do better on weekdays as that's when most people are in the office or are focused on working.

Similarly, weekdays were better to promote medical apps purchases.

The findings were based on a three-month study of app revenue and estimated weekly downloads for iOS applications that run January through March of this year.