They need to put the turkey in the oven at 4:30pm.
In order to determine this, we first need to add together all of the times that we are preparing the turkey.
45mins + 1hr and 30mins + 15min = 1 hr and 90mins or 2hrs and 30mins
Now, since we know it takes 2 hours and 30mins to prepare, we subtract 2 hours and 30 mins from the goal finish time of 6:30pm.
6:30pm - 2 hrs 30 mins = 4:00pm