Previously, Facebook said it expected the deal to close within the second quarter, which ends in June.
On Tuesday, the company updated its SEC filings to make the date less specific. It now expects the deal to close sometime in 2012.
The change follows reports that the FTC has launched a competition probe into the acquisition.
While the probe itself is routine for acquisitions larger than $68.2 million, the circumstances are not. Facebook is expected to go public at a $100 billion valuation later this week.
“Facebook is in the middle of the targets of antitrust enforcers,” David Balto, a former policy director at the FTC who now works as an anti-trust lawyer, told Mashable in an interview last week. “There are certain dominant firms that get the most intense scrutiny.”
Experts estimate FTC approval may take up to 12 months. In the meantime, Facebook cannot integrate Instagram technology or staff into its business.