How long can i put my baby (3 mths old) in carrier when out?

I use my Tula and Kokaidi baby carriers when we go out and sometimes my girl does fall asleep in it. If I didn't bring a stroller along then I let her nap inside, otherwise the moment she is in deep sleep I would put her in the stroller so she could nap inside instead. I will let her out of the baby carrier every two hours or so to feed and change her.