How to I make a cooldown like this or how do I get stacked "player's tool" to work?

[Duomax_]

So basically, I want a type of "booster" that lasts for 30 minutes, and I'm having 2 problems:

1) If the booster claiming item is a paper, the skript breaks if I stack the papers, any way to fix? If I make the "player's tool"/"player's held item" "player's tools" or "player's held items", it gives an error and if I replace the "is" with "are", it changes nothing, so how do I do this?

2) I can't get the time to work, I have no idea, honestly.. Like 30 minutes after you "claim", the variable that depicts the booster being active should be set to false, but if you "claim" it again, the time remaining of the "booster" should be extended by 30 minutes. I have no idea how to do this.. If I try, the booster never disables itself. Eg, if I set the variable {booster} to 30 minutes from now after claiming, the "%difference between {booster} and now%" never goes negative, and I can't disable it when its 0 either, I don't know why. because if I do 'while  difference between {booster} and now isn't 0: *booster effects*, It never stops, and keeps on going, forever..

For now, there is no perfectly working part of the skript, since the first part is claiming, which I have problems with, and the second part, the cooldown, I have no idea how to do. Please help!