No, you cannot have two tier 1 FPs scheduled at the same time.
Now, after the time slots have passed for all three of your booked FP+ and you have used at least one of them, you can book an additional FP+ at any in park kiosk and that new FP+ can be for a tier 1 attraction. But, availability will vary on park, day, time of day, crowd size, attraction, etc etc etc.
My guess is over the next few months you will see people pre-booking less Wishes/MSEP, etc to try and get an extra mid day or afternoon FP+, then around 2 pm they will rush to grab same day for the nighttime events.