About 20 people are currently living in the former car showroom on Iffley Road after moving in on New Year's Eve.
Leaseholder Midcounties Co-operative has said the squatters can stay until April, despite a judge granting it permission to evict them earlier.
But owner Oxford University's Wadham College said it requires the building back by 27 February.
This is so preparations for demolition can begin, the college said, as it intends to use the site for student housing.
Neo, a spokesman for the Iffley Open House campaign group, said it was "unacceptable" for the college to try to get the squatters out by February.
He added: "The weather will still be cold, I don't want people out on the streets."
The campaigners have asked that the building, which has been empty for two years, be officially designated as homeless housing.
Kevin Brown, group general manager at the Midcounties Co-operative, said in April the company has a legal obligation to hand the site back to Wadham College.
He added: "To ensure we're able to meet that requirement, we have been granted a repossession order but our preference is not to have to use it."
A Wadham College spokesperson said: "Whilst we have deep sympathy with the plight of homeless people, any solution must not delay the redevelopment of the building as homes for students.
"We will continue our discussions with all parties in the hope of resolving this amicably and are seeking help from local homeless support groups and charities to help find longer-term accommodation for these homeless people."

5 November 2015 Last updated at 17:26 GMT
It is a staggering number, and represents double the figure reported in April.
What is more it appears to dwarf the billion views YouTube clocks up daily, although it is not a true like-for-like comparison.
Facebook's aggressive push into video will surely delight advertisers who can promote their products alongside popular clips.
But YouTube star Tom Ridgewell - who has nearly four million followers on YouTube - told the BBC he was not convinced that Facebook was a big threat to Google's service.

Its youth wing was responsible for attacking and killing opposition supporters, the rights group said.
The CNDD-FDD party has not has yet commented on the allegation.
Burundi is recovering from a brutal civil war that ended with President Pierre Nkurunziza's election in 2005.
Speculation is rife that he intends to run for a third term in the June 2015 election, despite opposition claims that this would be in violation of the constitution which imposes a two-term limit.
The CNDD-FDD's youth wing, Imbonerakure, has "strong links to the security  services and are responsible for perpetrating human rights abuses with  impunity", Amnesty said in a report.
At least one opposition member was shot and killed by two soldiers on the orders of a local official and an Imbonerakure member, Amnesty said.
"Another opposition member had his teeth knocked out during a beating," the report said.
Squatters who turned an Oxford building into a homeless shelter have been given temporary permission to stay.
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More than eight billion videos are now viewed on Facebook every day, according to the social network.
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Burundi's ruling party is waging a "relentless campaign of intimidation" against its critics ahead of presidential elections next year, Amnesty International says.