If you want you can try my smartphone app for the 3BF start. It is a web page so it should work on any phone without installation.

It gives you a countdown (select your PHRF) using the phone's GPS

It will give you time and distance to the starting line too (the line's position is fixed and is hopefully pretty close to the actual line...) The line calculations are based on the line extending forever and where your GPS heading says you will cross it.

You must also turn on your phone's GPS (iphones call this "Location Services")
You must also give the route web page permission to access your location.

Works with most mobile browsers but they are all a little different and I have only tested on the phones I have access to. Let me know if you find a bug (errors get listed in the yellow box at the bottom of the screen).