A lead in time is needed so proper notice can be given- posters/signs will be put up, people without them can be given personal reminders rather than being turned away, people have time to make them and also get used to wearing them properly. Maybe a week's notice would have been enough.
Also I don't think it's urgent. Could easily have been a week later. I partly share PPs view about their limitations although I think they are of limited benefit rather than of no use. Many wearers don't use them properly- I see lots with them under their chins, touching them regularly, taking them down to speak, not covering noses and ignoring social distancing when they wear them.