After the seventh day, they stopped giving hearts altogether. Tried multiple days, no hearts. Not sure what the point was to continue the event after seven days.

I'm past day 7, and Reese won't give me anymore heart crystals.

Yes you can return anytime, as many as times as you want, by talking to Harvey. You can only get them from Reese/Cyrus, not from neighbors or anywhere else.

Can you get them from your neighbors too or just from Cyrus and Reese During this advent

I left the room, can I go back today?

yeah they will be

yeah they are on your mail

I used some of my heart crystals to buy 3 items but they weren't in my inventory. Will they be mailed to me?