Hi all,
When setting up 'resource dependant' activity with a duration of 5 days, then assigning 5 resources to the activity with a shared resource calendar of 4h/d (0800-1200).
Can one still get the activities start, finish & duration to not change as the below is doing?

no hence the name RESOURCE DEPENDENT. If you want to do this change the activity type to task dependent.
if an activity has been assigned as a resource dependent type of task then the duration will be based on availability for that resource to work on that activity and it will use the RESOURCES CALENDAR NOT the activity calendar.
Try to make the resource calendar as same as the activity calendar and it might do what you want.