I filled my car a week or so ago, not panic buying, it genuinely needed filling. It was probably 24-48 hours after those paying close attention to what was unfolding and thinking "just in case" would have gone out and topped up their car earlier than they would normally have done.
The garage has pay-at-the-pump overnight, and as I was paying the guy working there was on the phone to someone, saying how the first thing he does when he arrives in the morning is to look at the overnight sales.
"Three days sales in one night" was what he said.
The thing is if there is no real shortage, then when everybody has filled their tanks availability will return to normal.