"It will take us several months to draw out the conditions of an orderly withdrawal.so let's not waste time", he said.
Both have failed to reach an agreement to form an executive administration of the devolved government in Northern Ireland.
Irish nationalist party Sinn Fein said the prospect of a British agreement with the DUP was causing anxiety and fear.
Apart from the potential threat to peace in Northern Ireland, some members of the opposition Labour Party have spoken out against giving the DUP a formal role in the new United Kingdom government because of its regressive social views, including its opposition to same-sex marriage.
It is thought an announcement on an agreement will be delayed as a result of the Grenfell Tower tragedy and may not come until next week.
These concerns were echoed by former prime minister Sir John Major who has warned that the Government will compromise its stated impartiality if it enters a confidence and supply deal with the DUP at Westminster.
"Ultimately, I think the parties understand people voted in the March Assembly elections for a strong voice at Stormont".
The two leaders will discuss the progress of the talks to relaunch the North's power-sharing institutions and the forthcoming Brexit negotiations between the British Government and the European Union, which are scheduled to start next Monday.
The Irish republican Sinn Fein party which won seven seats in the election although MPs traditionally do not take up their seats in protest is also wary of the alliance.
While some members of her party have said she will have to go eventually, Ms May is expected to stay on as Prime Minister at least for now.
But May's predecessor, David Cameron, said there would be pressure after last week's surprise for a "softer" Brexit that gave greater priority to a close trading deal with the EU. The government should reserve all its energy for Brexit.
That would help safeguard jobs and trade with European Union members but would severely restrict the UK's ability to strike its own trade deals around the world.
When French President Emmanuel Macron met Mrs May in Paris on Tuesday, he said the door was open for Britain to remain a member of the European Union until talks ended.
He later told a meeting of his MPs that Mrs May had "no mandate and no legitimacy" and Labour would remain on an election footing in case the Government collapsed.
Discussions are going well with the government and we hope soon to be able to bring this work to a successful conclusion.
"The door of course is still open as long as Brexit negotiations have not been concluded", he said.