That would allow the Syrian government offensive to continue against Al-Qaeda-linked rebel groups in Idlib, the last province in Syria outside the control of Damascus.
Diplomats said the change could address Russia’s concerns over the proposed resolution demanding the ceasefire to allow urgent deliveries of humanitarian aid.
A vote on the measure is expected next week.
The council is considering the 30-day truce following a surge in violence across Syria, including in the rebel enclave of Eastern Ghouta where a government bombing campaign has killed more than 240 civilians in five days.
The draft resolution specifies that the ceasefire would go into effect 72 hours after adoption by the council.
Deliveries of urgently needed food and medical supplies would begin 48 hours after the start of the ceasefire as would medical evacuations, according to the text.
The measure would also call on all parties to immediately lift sieges, including in Eastern Ghouta, Yarmouk, Foua and Kefraya.
All sides in Syria must “cease depriving civilians of food and medicine indispensable to their survival,” and allow evacuations of Syrians who want to leave, said the text.
Striving for consensus
Negotiations on the draft resolution began last week after the council failed to back an appeal by UN aid officials for a month-long humanitarian pause in fighting.
Sweden and Kuwait, which lead efforts to address the Syrian humanitarian crisis at the Security Council, presented a first draft resolution on Friday.
Russian Ambassador Vassily Nebenzia last week said that it was “not realistic” to impose a ceasefire because armed groups fighting Syrian President Bashar al-Assad’s forces were unlikely to uphold it.
Russia has resorted to its veto power at the council 11 times to block resolutions targeting its Syrian ally.
As negotiations continued, Nebenzia told reporters on Wednesday that “we are striving for consensus,” suggesting that talks were progressing.
Air strikes hit a hospital in Idlib late Wednesday, the seventh such raid on a medical facility in two weeks, the Britain-based Syrian Observatory for Human Rights said.
Assad’s forces backed by Russian air power launched an offensive in December on Idlib, where the jihadists have expanded their control.
Some 2.5 million people, including more than one million displaced Syrians, live in the province.
More than 340,000 people have been killed in the nearly seven-year war, millions have been driven from their homes and 13 million Syrians are in need of urgent humanitarian aid.