Money that is paid in to the township treasurer for private connection rights under section 5 on or before the date specified pursuant to section 5(b) which creates an excess over the percentage of the net cost remaining after application of section 3 and money that is paid into the township treasurer for the rights after that date is excess money and shall be deposited in the contingent fund. This section applies to all money received by the township treasurer after May 19, 1941, in cases in which water mains, prior to May 20, 1941, were extended or installed in accordance with a plan substantially similar to that contemplated by section 5.