Standing Orders usually provide for meetings to be limited to 2 hours but you can resolve to extend that time if necessary. Your standing orders also usually limit the time allowed for public participation. Commonly this is for 15 minutes but can be longer and of course the key is whether your Chair is able to control the meeting appropriately and restrict the public from overrunning that time. If you've had a public meeting already there really isn't any justification for allowing the public to speak for any longer or to repeat what was said at the public meeting but it is for the Chair to control this.
You can end a meeting at the end of the allotted time of course and reschedule another meeting to complete the agenda. Don't forget, however, that there will need to be a new agenda, issued three clear days before the date of the resumed meeting. Personally not a fan of either overrunning or deferring items to a later meeting but I guess if needs must!