The fate of Wrightbus will be known in hours, Ian Paisley MP has said.
The Ballymena business was placed into administration last month and is up for sale.
The English industrialist Jo Bamford, son of JCB chairman Lord Bamford, is understood to have made a bid for the company.
However, the ownership of the Wrightbus factory, at Galgorm just outside Ballymena, remains a barrier to an overall resolution.
The premises are owned separately from the manufacturing business and held in a company called Whirlwind Property Two, which is not part of the Wrights group and is therefore not under the control of the administrator.
The property company is controlled by Jeff Wright, the former owner of Wrightbus.
Mr Paisley said the land remained the final hurdle to the deal, and Mr Bamford was not going to invest tens of millions of pounds if he did not control the asset.
“This is the last chance and I really hope that a deal can be done,” the Democratic Unionist Party MP said.
“The banks have accepted it, the administrators have accepted it and now the bell tolls for the landlord.
“At teatime tonight this deal effectively ceases to exist and sometime tomorrow I believe the administrator will be forced to liquidate this company.”
‘Do the right thing’
About 1,200 jobs were lost after the company failed to find a new owner before it went into administration.
The union, Unite, said the deadline to resolve the current impasse over site ownership was now 10:00 BST on Thursday.
“This is the eleventh hour in the effort to save these jobs,” said the union’s George Brash.
“Unite is calling on Jeff Wright to do the right thing – by this workforce, by their families, and by this town.”
Wrightbus went into administration last month after a period of financial difficulties.
Pre-administration attempts to sell the business were also complicated by the factory ownership issue.
The Wright family said it had not acted unreasonably during that sales process.
It said that one bidder had agreed to rent the factory, but then later withdrew the offer.