So far as I know, it is not obligatory to provide for public questions or comments, although it is highly desirable. It can be at any time, although often councils choose to place the public session near the start of the meeting.
The council of which I am a member provides a public session early in every meeting of the council and its committees. We have also amended our standing orders to allow the chairman discretion to permit public contributions in any part of the agenda. This, however, is probably unusual. Although it would be impractical for a large council, we have found it works very well for a small town council.