There has to be some sort of advanced notice for investor calls so that people have time to plan for it as some calls may impact investors either positively or negatively and for some that could mean millions ...
What about people who run companies or may be traveling etc ....

I'm not sure if this is defined in the sec rules ..but if no guidelines were given a company could just have a call on short notice for whatever reason .. Let's say bad news or Idk

Either way I think advance notice is appropriate and in this case allows for a few things to play out this week that will now be a part of the call