After manually changing Hello Interval to 3 and Dead Interval to 12, you must click Apply for OSPF adjacencies to form.
Dead Interval is, by default, 4x the Hello interval. Hello interval and Router Dead Interval configured in STC MUST match neighbor DUT routers. So, when you change the DUT Hello-interval to 3, then Dead interval becomes 12, and you must also change it on STC side.