The measure was passed in a vote of 67 to one with six abstentions.
The amendment was tabled by a special working group set up by the parliament to prepare for a dual citizenship referendum.
The Law on Referendum currently requires that a referendum be held no later than three months and no sooner than two months after the Seimas passes its resolution to call the plebiscite.
The amendment calls for holding a referendum no later than eight months and no sooner than two months after the date of the respective resolution.
Arvydas Nekrošius, deputy speaker of the Seimas, said the current time-frame was too short to properly prepare for a referendum.
MP Algirdas Sysas of the opposition Lithuanian Social Democratic Party, however, called the decision a "political game" aimed at influencing people's opinion in a dual citizenship referendum that is planned to be held in tandem with next May's presidential election.