Totally varies on how cold it is out there ... last winter we were able to go to the park most mornings and be outside from 9-11ish daily cause we did not have a lot of snow in our area and temperatures hovered around -3 mark or warmer so it was so nice out.
Unless it is colder than -10 or there is a weather warning in affect we make an attempt to get out daily and than play it by ear as to how long we stay out ~ I am a majority rules type person if all but 1-2 are voting to stay out we stay out and the others need to learn to toughen up and find a way to enjoy the outside ... if it is the non mobile infant having a really hard time than I will cut it short cause they cannot choose to keep warm the same way mobile children can.