Mr Sharif (l) and Mr Zardari - will they stand for parliament?
Pakistan's Election Commission has announced that delayed by-elections will now be held on 26 June.
The last date to submit nomination papers is 13 May, a spokesman said. Eight national assembly seats and 30 provincial ones are up for grabs.
Neither of Pakistan's top politicians, Asif Ali Zardari and Nawaz Sharif, ran in the February elections that saw President Musharraf's allies routed.
Some reports say they might consider standing in the by-elections.
The by-elections have already been delayed once and were due to be held on 18 June.
On Sunday the Election Commission said they had been put back even further, partly due to security concerns in the north-west. A new date of 18 August was given.
That prompted an outcry from Mr Zardari and Mr Sharif who said the move was undemocratic.
The Election Cmmission is staffed by presidential appointees. But a spokesman for Mr Musharraf denied that the delay was politically motivated, saying that he had had no involvement in the decision.
The by-elections are being held for a number of reasons.
Votes in some seats were postponed because of security concerns, in others because candidates had died, and in several more because candidates were successful in more than one constituency.
In that instance, they must choose which seat to represent, prompting by-elections elsewhere.