The merger was due to be completed on December 31, but the companies extended the date until the end of this month to allow for outstanding approvals.
With the approvals still outstanding, Glencore and Xstrata agreed to further extend the completion date until March 15.
Glencore said it was due to release its results on March 5 and the new completion date would give the companies the flexibility to complete the merger after the full-year numbers were released.
The deal looks close to getting regulatory approval in South Africa, with the country's main electricity supplier, Eskom, withdrawing its objections to the merger.
It came after the two signed a memorandum of understanding.
"The resolution achieved by the agreement establishes a framework within which Glencore and Eskom can co-operate with each other on a mutually beneficial basis and govern the interaction between them regarding existing and future coal supply agreements," Eskom said.
"In consequence of the agreement reached between the parties, Eskom has agreed to withdraw its intervention in the merger proceedings and that it no longer intends to participate further in the merger hearings."
The deal received Australian approval in July and European approval in November.