Is religion compatible with some worshippers having long nails filled with dirt? Is their ablution valid? Is there a specific time for trimming nails and other practices of the Sunan al-Fitra (practices of natural disposition)?

Nails must be taken care of before forty nights pass, due to the hadith narrated by Anas (may Allah be pleased with him): "A time limit was set for us concerning trimming the mustache, clipping the nails, plucking the armpit hair, and shaving the pubic hair: that we should not leave them for more than forty nights." Wudu' (ablution) is valid and is not invalidated by any slight dirt that may be under the nail.