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

We often carry my boy in the carrier out for the whole day. There would be breaks for feeds and diaper change after all. We love to head out and don't like to use strollers (mostly commute by bus and often without another adult). Agree with Jacq, don't see an issue with long durations of carry as long as both u and baby are comfortable.