I read that continuity is not necessary in Ghusl (ritual bath). So when I was performing Ghusl, I thought that I would take that whitish matter (that accumulates at the side of the toenails) out of my nails later on, when I would perform ablution for the prayer. Do I have to repeat my Ghusl because I intentionally delayed removing that from my feet? (As opposed to leaving something forgetfully.) I do not even know if water penetrates that substance or not. You may also know from my previous question that I suffer from Waswaas (obsessive doubts), so it is also possible that water went under it and that I am overthinking things. Do I still have to repeat my Ghusl because even though water would have reached under it, my intention was to delay washing it?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

Continuity in Ghusl is not obligatory according to the majority of the scholars. Hence, your Ghusl in the manner described in the question is valid and you are not required to repeat it, whether you observed continuity or neglected it, and whether you neglected it deliberately or forgetfully.

As for the whitish matter, if it part of the body cells or what it secretes of fats and the like; it is not considered a barrier, and it is not obligatory to remove it to begin with.

Our advice to you is to ignore Waswaas completely, as letting yourself get carried away with it leads to grave evils.

Allah knows best.