Over the past few months, Microsoft has admitted that developers who have submitted Windows Phone apps to the official App Hub have experienced longer wait times for those apps to be published in the Windows Phone Marketplace. While Microsoft has made some improvements to these publishing times, it warned that planned improvements to the back end of the App Hub and Marketplace could reduce those publishing times again until they are in place.
Today, in a new post on the official Windows Phone blog, Microsoft said that Windows Phone app makers who have apps ready to be submitted should do so either today or Tuesday, due to their planned upgrades. It stated, "While maintenance work is underway you may experience delays in app certification and publishing."
It added that the App Hub itself will be going down the morning (Pacific Time) of Monday, August 6th, in order for Microsoft to install these new back end improvements. The downtime should be less than 24 hours. Microsoft states, "Rest assured our teams will be working as quickly as possible to minimize the impact on you. Once the developer portal is back online, you might still encounter an occasional hiccup as we complete the back-end work over the next several weeks."
Microsoft says that all of these improvements should, when fully put into place, " ... result in a more robust submission and certification pipeline for your Windows Phone 7.5 apps..."
Source: Official Windows Phone blog