The scp cannot contain other things which are similar to it, e.g, another box or just cardboard.
How would anyone figure out these exact mechanics? How would anyone figure out that the box is anomalous to begin with?
it CAN contain another scp, just up to a few days though,
Plenty of regular cardboard boxes can also "contain" Safe-class SCP objects.
it it were to go against the set time, then it will be in a loop of being contained, and destroyed, for the amount of days it contained the other item, and the amount of time it passed that specific time, then it will be reconstructed.
I'm not sure I understand this. Why would there be a loop? What is being destroyed during the loop? What if a sapient entity in the box just opens the box and walks out without destroying it?
Personally, I don't think this will do too well on the site because it's just a generic object with a generic effect, conveniently tailored specifically to the Foundation's modus operandi for… some reason. I suggest reading over this essay on common SCP pitfalls to get an idea of what elements to avoid putting in an SCP article, before revising your premise here.
