Do not advance my due date?

Trying to pay some extra towards my loans and I am incredibly confused by this wording “do not advance my due date more than one month, even though I’m paying more than the current amount due” (nelnet if that matters)

My main question is: if I don’t check this, does it still apply all the money immediately, and do you have an official source somewhere that says this.

I think I understand that like if you pay a bunch of pauses payments and just counts those as good, and so it’s good to keep making payments on it instead of just making big payments every so often, and you’re probably going to have to configure the auto debit manually to make sure you’re still making payments consistently (which I would appreciate info on if anyone has, haven’t started repaying yet still in grace period)

And people have said it’s better to not check the box to give yourself some slack in case anything goes wrong AS LONG AS YOU PLAN TO MAKE CONSISTENT PAYMENTS AND NOT PRETEND IT DOESNT EXIST ANYMORE which I obviously pan to do.

Planning on trying to pay this specific loan off in the next year or two if possible bcuz the interest rate is so high (6.5ish) so idk if like not checking the box would cause some sort of issue where even if I pay it all off in a year it thinks I still have payments for years? Or if it’s just fine and says it’s done as long as money has been met