Most often, croup lasts 5 to 6 days and becomes worse at night. The croupy cough can last up to 2 weeks

If you see a GP and are prescribed redi-pred, it should be gone by day 3/4.
We have tried to ride it out (roughly 5 days) but always needs meds

Croup can last between 2 to 5 days, but sometimes they can have a cough that can last for a couple of weeks afterwards.
My daughter seems to get croup every time when she gets a simple cold, most times she ends up getting prescribed Predmix (steroids) to help open her airways.
It worsens at night time, so I make sure her head is elevated while she sleeps.

The general time duration of symptoms lasts from 2 days up to 5 days. Symptoms at night-time can worsen, and in my personal experience, it certainly does worsen at night.