It all depends on the chick. Many of the chicks that pip at the wrong end take longer to hatch because the time that they would have been learning to breath is not happening in the air cell. So be sure to give it a little longer before you think of any type of assistance. I believe on chicks it’s around 18 hours, on ducklings it 24- 36.
i would search for the guide to assisting on hatches by @Pyxis its has details on this type of hatch.