find a recent hack to "amature" convert that has played more than 5 rounds and it's quite easy to work out
search amateurs on the community page
the first person on the list played 9 rounds at hack before advancing
sum of best 5 wgt average
5th round 480 96
6th round 470 94
7th round 464 92.8
8th round 458 91.6
9th round 446 89.2
10th round is played at amateur
so it's safe to assume that the required average to tier up to amateur is 90