This blog post of Yochay Kiriaty is a good read to those of you who want to gain a better understanding of the Windows Phone Silverlight Application loading time requirements.
Source: The Windows Phone Developer Blog
By design, your Windows Phone application should load and run (display something to the user) as soon as possible—not simply to comply with the Windows Phone Marketplace certification process, but primarily to ensure a better user experience. Users hate to wait for an application to load on their mobile devices. For example, if your application takes eight seconds to load, you can expect some user frustrations. While eight seconds may not sound like a lot of time, one of the Windows Phone Marketplace certification requirements is for your application to display something besides the built in Silverlight splash screen in no more than five seconds. If that is not a good enough reason for you to optimize your application’s load times, don’t forget that users can simply press the Start button and effectively exit your application before it completes its loading process.