Minn. Stat. § 317A.221: RESIGNATION.

(a) A director may resign at any time by giving written notice to the corporation. The resignation is effective without acceptance when the notice is given to the corporation, unless a later effective time is specified in the notice.

(b) If a resignation is made effective at a later date, the board may fill the pending vacancy before the effective date if the board provides that the successor does not take office until the effective date.