How do I start keynote timer on first slide

This question was originally asked and answered here: https://discussions.apple.com/thread/7718522

An alternative answer, easier and cleaner in my opinion, is to simply copy your first slide and then paste the copy (as insert) right after itself. You will then have two identical slides at the front of your presentation.

Once you play the presentation, click to start the timer. The slideshow will advance to slide two but, since it is identical to slide one, no one will notice.