Seeing how pretty much every possible reward is found on almost every possible donation value and delay time, I can't help but think this actually works the sme way as the chance time/gacha algorithm:

1. Generate a random value from 0% to 100%.
2. Fetch the correct set of (Delay Time, Nut/Color Category) from the table, based on RNG and Donation.
3. Generate a random value from 0% to 100%.
4. Fetch the correct set of reward items from the table, based on RNG and (Delay, Nut) set.

The first two are executed when donating, the last two when fetching the rewards.
The bigger the donation size, the higher the chance for bigger (Delay, Nut) sets (Like stepping-up in Chance Time).
The bigger the (Delay, Nut) set, the higher the chance for better rewards.