How to write build time stamp into apk

Question

1. Making some changes in Android Contacts package
2. Using mm (make) command to build this application

Because I have to change and

Answer 1

So Android Developer - Android Studio User Guide - Gradle Tips and Recipes - Simplify App Development actually documents what to add in order to have a release timestamp available to your app:

android {
  ...
  buildTypes {
    release {
      // These values are defined only for the release build, which
      // is typically used for full builds and continuous builds.
      buildConfigField("String", "BUILD_TIME", "\"${minutesSinceEpoch}\"")
      resValue("string", "build_time", "${minutesSinceEpoch}")
      ...
    }
    debug {
      // Use static values for incremental builds to ensure that
      // resource files and BuildConfig aren't rebuilt with each run.
      // If they were dynamic, they would prevent certain benefits of
      // Instant Run as well as Gradle UP-TO-DATE checks.
      buildConfigField("String", "BUILD_TIME", "\"0\"")
      resValue("string", "build_time", "0")
    }
  }
}
...

In your app code, you can access the properties as follows:

...
Log.i(TAG, BuildConfig.BUILD_TIME);
Log.i(TAG, getString(R.string.build_time));

I'm including this here since all of the other solutions appear to be from before the official example.