I recently updated to Android Studio 2.3, and now when I try to run the application, the emulator does not come online. It times out after 300 seconds.
Additionally,
For Linux users using KVM and facing this problem try setting the Graphics option on the Android Virtual Device to Software instead of Automatic or Hardware . As previously mentioned in this answer.
I can confirm that the method works for Arch Linux, Ubuntu 16.04, as well as windows with or without a proprietary graphics card using Android Studio version 2.3.1+