The commissioners shall, for the purposes of this or the special Act, have power, by themselves or their officers, to enter at all reasonable hours in the daytime into and upon any buildings or lands within the limits of the special Act, as well for the purpose of inspection as for the purpose of executing any work authorized to be executed by them under this or the special Act, or any Act incorporated therewith, without being liable to any legal proceedings on account thereof: Provided always, that, except when herein or in the special Act it is otherwise provided, the commissioners or their officers shall not make any such entry, unless with the consent of the occupier, until after the expiration of twenty-four hours notice for that purpose given to the occupier.