I had the same reaction as you, so I googled it.  According to Wikipedia[1] the eruption did indeed take two days, with shocks starting in the morning and ash starting to fall in earnest at 1 p.m., with &quot;pyrocastic flows&quot; beginning in the middle of the night.  People were able to escape and be rescued during the afternoon.<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Eruption_of_Mount_Vesuvius_in_79#Nature_of_the_eruption" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Eruption_of_Mount_Vesuvius_in_...</a>