No Tiaras before 6 pm.
There is maybe a symbol of royalty, but still, we have never seen Kate Middleton or the Queen herself wearing the tiaras while making official public appearances during the day. This is because they consider tiaras to be very formal and so should we wear them at night, particularly after 6:00 pm.
As they consider wearing tiaras way too fancy to be wanting during the day and so for that, they have to wear regular hats during the day as we have often seen Kate and the Queen. Not only this but there are their indications of the marital status of the royal members as they signal that the woman has been taken and perhaps this is the reason Meghan received her Crown on her wedding day.