If Doctor Evil was custom-designing a virus to infect as many people as possible, this sequence would be almost ideal for the purpose.
MUCH more effective than the fictional nerve toxin in Close Encounters of the Third Kind; the toxin in the story line taking effect almost immediately, as well as missing having no transmission human-to-human capabilities.
A better analogy would be The Mockingjay, part 2, where at the gates of President Snow's mansion the first bomb blast creates a selection of wounded victims, and the second blast hours later takes out the first responders plus good people helping out as well as survivors of the initial blast.
According to the CDC, people can spread influenza for 3-4 days before they show symptoms. From a variety of sources:
For mumps, the contagious period can start 7 days before symptoms show. Ditto for German measles. Hepatitis A can be communicated up to 14 days before the onset of jaundice. Scabies can be spread 4-8 weeks before symptoms appear.
It is hard to find information on infectious periods before symptoms appear. I suspect the only reason Covid-19 information is so readily found is because it’s news. Another thing to consider is that knowledge of this disease is evolving rapidly. Yesterday’s theory may be discredited today, but it’s still on the Internet.