It means if you are planing to get the Super Rare in any of those new time limited treasure, you have to use all 210 seal scrolls during the period (2 weeks) that they are on.

If you go like, i have 190 seal scrolls i will use them this time and wait until next time the treasure appear and use the remaining 20 seals to get my SR, what will happens is that the previous 190 seal count will be reset back to 0, and you will have to use another 210 seal (again all at once) to get your SR.

Long story short, DON'T use seal scrolls on them unless you have enough to pull the super rare (which can vary with some luck between (200 and 250 seals).