wa 'alaikumsalaam, what l've learnt max. time for darah nifas can be up to 60 days (according to mazhab As-Syafie -. and theres a method to specify whether its still nifas or haid. Hence, each person varies. U may want to follow /learn from Ustzh Nadia Hanim.
Likewise, theres an exceptional too for breastfeeding mum on which we can bayar later on. Be it in a form of fidyah / & qadho' depending on the situation. wAllah a'lam.