You have to purchase during the event cycle dates in order to collect. You then get rewards for the next 6 days, no matter what day you buy it on. Even if you buy it on the last day of the cycle it will let you collect all 7 (1 initial + additional 6 days) days worth. You cannot deposit after the cycle ends, even though you will still see the event. After the 6th day when the event ends, the icon will disappear until next time.

tl;dr: as long as you deposit during the 18th-24th, you can collect all rewards.