Data points:
I applied in July, got approved for the world mastercard and got initial bonus by spending a few dollars. I only used the card once. At the end of October received offer (via both email and regular mail) for 15k bonus by spending $751 in Nov, Dec and Jan .
Wife applied in August. She was only approved for the platinum card, but the bonus amount was the same. She got the 15k bonus offer in late Nov for Dec, Jan, Feb spending.
Seems like the