I would like to be able to use a form that people can fill in to clock their hours manually.
i would like the date/time field to automatically be set to today and a specific time like 8am for start of day and 6pm for end of day. the user then can modify from there when filling in.
Unfortunately, form view does not currently support dynamic default values, sorry 
You would need to add text or number fields where the user could define the start and end times, and a script to convert those to proper DateTime field(s). Pretty kludgy though.