You can't.
Android needs to start a lot of services, and your app is just one of them. I believe system apps are started first(Google Play Services, for example) and after that all 'normal' apps will start. This'll take a few seconds after the device shows it's lockscreen. But when Android shows a lockscreen, it doesn't mean that it completely finished booting. It finished it system boot, but app services(like your app) still need to start. Most of the time, it's just for setting a scheduled Alarm or se, and there's no need to let the user wait an additional couple of seconds before he is able to use his device.