Time is running out for taxpayers eager to get a jump on their property taxes before changes recently passed by Congress kick in -- but in Cook County, office hours are being extended to give them a hand.

And while Cook County Treasurer Maria Pappas said prepayments will indeed be eligible for an increased deduction on homeowners' 2017 federal tax returns, not all counties' officials are certain.

Pappas said her office at 118 N. Clark St., Room 112, in Chicago will be open from 9 a.m. to 5 p.m. on Sunday, New Year's Eve, for those wanting to pay in-person on the final day. After 5 p.m., payment can be dropped off in a mailbox set up next to the door to Pappas's office.

Payments will be honored provided they are made or dropped off before midnight Sunday.

Officials in DuPage, Kane, Lake and Will counties, however, were not opening on the weekend; there, today is the last day to pay.

In Illinois and elsewhere, local officials had told residents that property taxes due next year could be prepaid through the end of this year; that way, the full amount paid this year could still be deducted on 2017 returns filed next year typically by mid-April.

But an IRS advisory issued Wednesday appeared to throw a monkey wrench into the works. The directive, which some found confusing, drew a distinction between paying an estimated amount and paying exact amounts on assessments made before 2018.

This may be straightforward -- or not. Cook, DuPage and other counties in 2017 completed new assessments to be applied to property tax bills mailed in 2018.

Pappas has seen the new IRS advisory and said Cook County residents who prepay will not be affected.

"There's no guessing what the amount is. This is an exact bill," she said.

Kane County Treasurer David Rickert was less certain.

"We will have to see what the IRS does," said Rickert, a Republican. "I don't want to speculate on what the IRS will do. I will venture a guess that Congress will probably find a way to address this down the road."

• This report was produced in partnership with the Chicago Sun-Times. See a full story plus another take on property taxes at chicago.suntimes.com.