The Rambam (pesulei hamukdashin 19:2) writes that any korban that is questionable whether it became passul, requires עבור צורה before burning it - meaning that it must sit overnight which renders it passul as no'sar, and then it can be burned. However, the gemara poses a series of questions whether the פרים הנשרפין would become passul such as whether their is a p'sul of sitting overnight, whether there is a p'sul of being taken out of the courtyard and when part of if was taken out together with the majority of one of the limbs. The Rambam paskens that since the gemara leaves with a תיקו in all these cases, we have to be machmir to assume that they became passul and are burned in the courtyard (which is where you burn kodshim that became passul). The Rambam then adds that although when there is a safeik whether it became passul it would normally require עיבור צורה which means to sit overnight, that is only by regular kodshim that is not supposed to be burned and is therefore considered degrading to burn it. But, the פרים ושעירים הנשרפים which are supposed to be burned even if they didn't become passul, the only issue is where to burn them, do not require עיבור צורה [since they are supposed to be burned anyway, the burning of them isn't considered a בזיון קדשים - kesef mishnah quoting maha'ri kurkos].
The Minchas Chinuch (mitzvah 143) raises an interesting question. Normally the function of עיבור צורה is that since until now it is only questionably passul, we can't burn it until עיבור צורה which makes it definitively passul. However, since one of the question in the gemara is whether sitting overnight would create a status of no'sar invalidating the פרים הנשרפין, the concept of עיבור צורה doesn't apply. The Rambam shouldn't need to give the answer that he gives, rather he should say that sitting overnight doesn't accomplish anything by these korbanos - why would it help to sit overnight since one way or the other it would only be questionable whether it became passul? The Minchas Chinuch answers that since there is another safeik whether it became passul, sitting overnight would be an additional safeik. There would be reason to wait another night so that there is a double safeik whether it became passul before burning it, and that is why the Rambam had to say that the reason it doesn't need עיבור צורה is because even if it is kasher it is meant to be burnt so that the burning isn't degrading for it. The difficulty with the answer of the Minchas Chinuch is that the Rambam seems to require the reason that he gives even for the case where it already sat overnight. In the case where it sat overnight, it certainly wouldn't accomplish anything to let it sit overnight again, yet the Rambam gives his reason as to why it would be burnt immediately.