The sale will last during:
Sale Start Day and Time: 5pm PDT/ 8pm Eastern September 26/ 2am EU
Sale End Day and Time: 12am PDT (midnight)/ 3am Eastern/ 9am EU
During this time if you buy 1 MMC you get another free, if you buy 10 MMC you’ll get 10 for free.
I recomend to buy them now if you can’t wait for it, otherwise it would be better to wait for the next update in wich MCC will be available to farm throgh Wanted Board quests every 2 hours.