To get the time at which your app was installed or updated, you should query Android’s package manager.

try {
    // Reference to Android's package manager
    PackageManager packageManager = this.getPackageManager();

    // Getting package info of this application
    PackageInfo info = packageManager.getPackageInfo(this.getPackageName(), 0);

    // Install time. Units are as per currentTimeMillis().
    info.firstInstallTime

    // Last update time. Units are as per currentTimeMillis().
    info.lastUpdateTime

} catch (NameNotFoundException e) {
    // Handle the exception
}