After chemically straightening hair, why would I need to wait 3 days before washing my hair?

Also, How long does it take to get old hair back?

After chemically straightening hair, why would I need to wait 3 days before washing my hair?

Because there is a chemical called thioglycolate in a straightener... Same rules apply with a perm because they share the same ingredient... If you wash your hair you will break down the bonds and revert your hair back to frizzy or curly... So wait at least 48 hours! Touch ups depend on the degree of your curliness... I would say every month to 3 months... which is nice since it will only be a retouch therefor only your outgrowth will be receiving the treatment! Once you can wash your hair again give yourself a deep conditioning treatment!

After chemically straightening hair, why would I need to wait 3 days before washing my hair?

you need to wait three days , so you don't wash away the chemicals.if you washed your hair then the treatment wouldn't really work. The answer to your other questions is six months.