Level Six is only minor and major 3rds. I am constantly reviewing this concept with the major and minor chords. This level and level three (whole steps and half steps) gets very repetitive unless you separate the cards into up and down piles. I find that if we go up and then down, we aren't moving to the same two or three notes. With this in mind, you can use just the "hop up" cards to race up the piano or the "hop down" cards to race down.
Usually when racing I start at the far end of the piano and race to middle C. I put a little sticky flag on the note and whoever gets to the flag first wins. Now "Hop" to it!
Google Docs: Hopping Intervals Level Five: 2nd-8th
Hopping Intervals Level Five
Google Docs: Hopping Intervals Level Six: Minor and Major 3rds