Chargebacks are processed depending on departure date. This is in direct relation to the timeline for chargeback submission set out by the schemes. The closer the date of the chargeback, the higher the priority of submission.
These are outlined here for each scheme:
MasterCard (https://chargeback.com/mastercard-chargeback-time-limits/)
Visa (https://chargeback.com/visa-chargeback-time-limits/)