In comments made to the national parliament on Wednesday, Spanish PM Mariano Rajoy said he would not extend the deadline to wait for a clear answer from Catalonia's president, Carles Puigdemont.
"This requirement is firm and it expires in less than 24 hours and if this is not dealt with, Mr Puigdemont will provoke the application of Article 155 (of the constitution)," Rajoy said.
Invoking Article 155 allows the central government to take back control of regions, such as Catalonia and the Basque Country, that were granted sweeping freedoms after the 1975 downfall of the Franco dictatorship -- if they acted beyond the law or threaten the national interest.
Such a step would almost certainly mean officers from the Guardia Civil, the national security force, being deployed once again in the streets of Catalonia, a provocative act that risks sparking violence.
Shortly after the October 1 referendum -- in which 90% of ballots cast in what Madrid termed an illegal ballot were in favor of independence -- Puigdemont walked back on his pledge to take Catalonia out of Spain, saying that he was instead suspending the declaration in the hopes of talks
It is unclear what shape those talks might take, or who would mediate them.
The referendum, marred by violence as Spanish police closed polling stations and dragged away Catalans attempting to vote, had a turnout of only 43% of the voter roll -- which Catalan officials blamed on the central government's efforts to stop the vote.
The violent clashes left almost 900 people injured, according to Catalan officials.
Tens of thousands of people joined a candlelight vigil in Barcelona earlier in the week to protest the detention of two Catalan separatists.
On Monday, Spain's High Court ordered the head of the Catalan National Assembly (ANC), Jordi Sanchez, and the head of Omnium Cultural, Jordi Cuixart, be remanded in custody while they continue to be investigated for sedition.
Footage of Tuesday night's rally in Barcelona shows protesters holding up placards calling for the pair to be freed. They also held up signs saying: "Save Europe" and "Help Catalonia."
Time to make a choice
On Wednesday, Rajoy said the time for Puigdemont's vacillation on the independence question was over.
"The only thing I am asking Mr Puigdemont is that he acts with sanity, that he acts with balance, that he puts the interests of all citizens first, of all Spaniards and all Catalans.
"It is not difficult to answer the question 'have you declared Catalonia's independence or not?'"
He said that if the Catalan government was to unilaterally declare the breakaway, the central government would be constitutionally "obliged" to respond "in a certain way," possibly indicating the activation of Article 155.
"If he hasn't (declared independence) then we can discuss it here in parliament which we, all the parliamentary groups, have offered to do."
Going it alone?
An independent Catalonia would have few friends, with other EU countries fearing breakaway movements as well. In any case, under EU rules, Catalonia would not be a member of the EU on its own, and would have to apply for membership from outside the bloc.
On Tuesday, Rajoy spoke to British Prime Minister Teresa May, who told him that her government would not recognize an independent Catalonia.
"The Prime Minister reiterated that the UK is clear that the referendum had no legal basis and that any unilateral declaration of independence would be inconsistent with the rule of law," according to a Downing Street spokesperson.
"She added that the UK would not recognize any such declaration of independence by Catalonia."