You can receive the Eucharist twice in one day if the second time is at a mass and not a communion service:
Can. 917
A person who has already received the Most Holy Eucharist can receive it a second time on the same day only within the eucharistic celebration in which the person participates, without prejudice to the prescript of can. 921, §2.
Canon 921 refers to Viaticum. It is possible that you go to two masses in one day, then are in a situation to receive Viaticum, and that is allowed. It's the only way you can receive the Eucharist 3 times in one 24 hour period!
Whoops! I guess I was wrong. When our Festival Choir sings both Masses at Easter, we always receive at only one. This past Easter, the Extraordinary Minister of the Eucharist forgot to bring Communion to us up in the Choir loft. They usually do that because there are so many people at Mass, it's difficult for us to get downstairs to receive, then back up again to sing. I'm an Extraordinary Minister also, so I brought it up for us so we could receive before singing the Communion Hymn.
How is the term "day" defined, for such purposes? Local midnight to local midnight, typical sleep/wake cycle [excluding all-nighters and naps], or what? I would think the latter definition would be the most logical, excluding deliberate abuse.