https://www.w3schools.com/PhP/func_date_interval_create_from_date_string.asp
Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java, XML...
date intervalstring functionphpcreate
https://www.sap.com/design-system/fiori-design-web/v1-71/ui-elements/calendar-date-interval/
The calendar date interval control displays a range of days in a single row, saving on horizontal space.
calendar dateinterval