It could be just a hello world, but it should be initialized in milliseconds and be lightweight to download (1mb max).
If it's actually going to be an app I guess writing something against the NDK in C++ would be the fastest option?
No code is faster than no code.
it already exist, you don't even need a phone to install it on. milliseconds isn't that great of expectations. Think nanoseconds, close your eyes, let it pop. Do you see it?