How to set the default time to 7 AM for Date/Time Field

Try this:

var dt = new Date('{!#TODAY}'); dt.setHours(7,0,0,0); //Change {!#TODAY} to whatever you need it to be

rbf_setFieldValue('dateTimeField',dt); //As long as it's a date object that has it's time set to whatever you need it to be it should work

This should work.