A legal challenge under this chapter shall be filed within 30 days from the date of a meeting which is open, or within 30 days from the discovery of any action that occurred at a meeting which was not open at which this chapter was violated, provided that, in the case of a meeting which was not open, no legal challenge may be commenced more than one year from the date of said meeting. The court may enjoin any challenged action until a judicial determination of the legality of the meeting at which the action was adopted is reached. Should the court determine that the meeting did not meet the requirements of this chapter, it may in its discretion find that any or all official action taken at the meeting shall be invalid. Should the court determine that the meeting met the requirements of this chapter, all official action taken at the meeting shall be fully effective.