When writing mobile applications over Flex 4.5.1, your application may be running in the background, even when pressing the back or home buttons on your device. This may become a problem if your application is doing things using timers, making server calls etc.
When developing mobile applications with Flex 4.5.1 you are always going to have a short time until the application loads.
It is very recommended to add a splash screen to your application to ease the wait and improve the User Experience.
Christophe Coenraets, Adobe evangelist, published a very interesting post about charting on mobile platforms.
You can read more about it here.