So, the standard default Date Picker or Date Time Picker does not meet your requirements.
For Instance level, configurations are passed as arguments to "NewCssCal" function. you can have MORE THAN ONE patterns in ONE single web page. For instance, you can have first input for user to pick a birth date, another one input for user to pick a date and time for appointment to be made.
On the other hand, configuration is made in "datetimepicker_css.js" for File Level, whatever changes that you made, it is going to affect every date picker or date time picker you have in your web page. Configurations such as preferred Weekend color, first year in of Calendar, whether or not you allow user to pick a date from the past are File Level Configuration.