I'm sure this must be an Idea already... I can't find it. And as far as i am aware it is not out-of-the-box functionality.
In ArcGIS Online and Web AppBuilder Edit and Smart Editor widgets, it would be valuable to be able to set the default date to now or today. We have users enter records through a web app and its a hassle to have to open the calendar and select the date (which is always the current date).