The process for opening up a branch on a business day when it was previously closed is in the Illinois Promissory Note and Bank Holiday Act. We recommend that you review subsection (b), where you will find the requirements for closing and opening a branch on a business day. As to reopening a branch on a business day, that section states:
Any such selection shall remain in full force and effect until a copy of the later resolution of the board of directors of such bank, certified in like manner, terminating or altering any such prior selection shall be filed and published in the same manner as such prior resolution.
In summary, the board of directors must prepare a resolution that terminates their prior resolution to close that branch on Thursday. The resolution must be certified by an officer in charge of the bank’s records. Further, the Act requires you to file the certified copy of the resolution with the county recorder and publish it once a week for three successive weeks in a newspaper of general circulation in that county.
I actually just inquired about this and this is the answer that I received from IBA. Hope it helps!