If your informal meeting is open to the public, why not call it an additional meeting of the council? If you're not operating under standing orders, you have no right to exercise the normal controls over the proceedings, so if members of the public decide to take over the meeting to lobby for their own projects, there is nothing you can do about it. Standing orders exist to protect the council, as well as govern its business.
For the record, two of my councils meet bi-monthly, but still get through all of the business in under 2½ hours. We don't allow verbal reporting; everything is written down and circulated beforehand. All papers are taken as read. The report author has an opportunity to add anything they consider relevant (but not to read out or summarise the written report) then members may ask questions. Occasionally this will take five or ten minutes, but the average is far less, then straight to a vote on the recommendations of the report and we move on.
If you wish to educate the public about local government finance regulations, which is a very worthwhile objective, why not have 15 minutes of this at the Annual Assembly?