The mirrors receive update files, and synchronizing all of that takes time. If the update was released at that exact moment and you want to install a file, it won’t work, your local database is then not current. (simple explanation)
No → only with regard to this command paru -Syyu
I never use this command. We have thx @the devs / team from garuda the garuda-update to do this or the handy script gun.sh from tbg. (this, of course on your own risk, but this script is running well)