Some data on first run tournaments
Gigantophis (2/25/19) was just before we started tracking tournaments and was exactly 3 days
Lythronax (3/18/19) had rules and was exactly 3 days but required 1167 trophies
Mastodon (7/1/19) required Mods and 1109 trophies and lasted for 4 days, 4 hours
Suchodus (7/29/19) lasted for 3 days, 4 hours and required 1415 trophies.
Eucladoceros (12/23/19) lasted for 3 days, 4 hours and required 1354 trophies. It had been out in the wild for a bit before this tournament.
Dracorex (3/2/20) lasted for 3 days, 5 hours. The bottom of dominator league ranged from 1397-1682 trophies.
Plesiosuchus (4/20/20) lasted for three days, five hours and required 1500 trophies
So, we really have five comparable data points covering a wide range. At the absolute minimum, I would go for 1450 trophies and 1700+ would be much safer. It just depends on how much you think those top scores on Dracorex were outliers.
The above prediction assumes the upcoming tournament is in the three day range. If it is a four day plus tournament, aim higher, at least 1800 trophies. Assuming this tournament is indeed for the much in demand Brachiosaurus, this tournament MAY run even faster. We shall see.