For the previous similar WMC promos (2 rounds of campaign so far), I received cashback for all my eligible spending for every month, even those done right at the end of the month. At that time, WMC was not a very popular card (probably due to AF, which is now removed).

For this new 10% promo, I have not received the cashback for January spending yet. Based on the previous promo, it is usually paid out at the end of the next month. For example, spend in Jan, receive in late February. However, the payout date is totally random and I will usually report here when I receive the payout.