What is the rise / fall / feed cycle of a sourdough starter? I'm following this recipe to make a sourdough starter for the first time.

The recipe says to wait 3 days before the first feed.
On the morning of day 2, the starter had increased 3 times in size.
By the evening of day 2, it had reduced in size back to about 2 times the original volume.

My question is: what's the best way to judge when to feed the starter?  If it is reducing in size now, does that mean it is "hungry" and running out of food?  Or should we expect a couple of rise &amp; fall cycles before the first feed?

Is feeding time best judged by time elapsed, or by volume of the starter?
For sure this method will work, but it can be risky starting with grapes as you're introducing more than just airborne wild yeasts. With so many bacteria strains active in a new starter, it very well might rise and fall multiple times, but an established starter will have one rise and fall cycle every 12-24 hours unrefrigerated, and then will need feeding.