There are a total 5 stages in Kuriboh evolution, including its most basic form. During each of these stages, you can choose to release your Kuriboh in order to obtain the corresponding Gift as per mentioned below. However, if you released your Kuriboh, you will not get another Kuriboh to evolve, throughout the duration of the event, so it might be wise to release your Kuriboh at the corresponding Gift you want to take, some tips here which you should know, are:
1. Ticket Rewards
The list of card rewards are the same for Sphere Kuriboh, Relinkuriboh, Kuribohrn, the difference is the foil quality of the card (Normal / Glossy / Prismatic), obviously Prismatic being the best choice. You are able to redeem this card according to your choice.
2. Rainbow Pack
The Rainbow pack at Kuribandit is a SR/UR card that is selected randomly from the list of SR/UR cards obtainable from Sphere Kuriboh, Relinkuriboh and Kuribohrn, therefore making this selection an inferior choice because you will not be able to choose the cards to redeem.
3. Duel Point
Although it is listed you can gain different amount of points depending on the type of duels you play (Ranked, Special, Casual, Duel World), the earning is only calculated on your very first duel after daily reset. So in order to gain 300 points, your first duel after reset must be either Ranked/Special Duels, or you can choose the x3 standard multiplier when dueling standard duelists, otherwise you will only gain 100 points and will not further gain extra points until next reset.
Duel World Duels
4. Kuriboh's Form and Rewards
You can only receive 1 Gift depending on which Kuriboh evolution you released, the Gifts are not accumulative.
Probably a combination of people screwing up on the first Kuriboh due to unclear instructions and them having intended the last-tier Kuriboh to be a "perfect run" (IE, playing every day) and gave too much leeway.
I wouldn't be shocked if they had always planned the second Kuriboh on to be a smaller time period.