Is it somehow possible to set Android to standby-mode programmatically ?
If you're developing your own ROM or you have a rooted phone (it's need to be checked which user is able to do this) then you should have a look to the PowerManager.goToSleep functionality. Here is a discussion about this function in the Google Groups. And here you can read about this particular permission.
This functionality has been removed since API level 21: https://developer.android.com/sdk/api_diff/21/changes/android.os.PowerManager.html
Like Yury also mentioned, before you were able to call powerManager.goToSleep(time)
, but you would have needed a rooted device or app would have needed to be signed as a system app to acquire the relevant rights.
http://developer.android.com/reference/android/os/PowerManager.html#goToSleep%28long%29
This is what i think you are looking for. Don't forget to include following permission.
android.permission.DEVICE_POWER