Setting clocks forward by an hour, to six hours ahead of GMT, should enable the country to take advantage of an extra hour of daylight in the evenings and save power.
Shopping centers have also been ordered to close at 9 p.m.
while government offices have been told not to turn on the air conditioning for the first three hours of the working day.
Pakistan tried moving to daylight saving time in 2002, but abandoned it as many people, particularly in rural areas, ignored the switch.
Some people doubted the time change would work this time.
"It's bound to fail. Half the people aren't aware of it and the other half don't care," said Adnan Hadi, a television producer in the southeastern city of Multan.
Pakistan is grappling with a shortfall of 4,500 MW of power and throughout the country electricity is cut, usually for an hour at a time, several times a day.
Water and Power Minister Raja Pervez Ashraf said on the weekend the government planned to overcome power shortages within a year by generating an extra 6,000 MW.
He did not elaborate on how the extra power would be generated but officials have said Pakistan hoped to import second-hand generating equipment.
Power cuts, as well as food shortages and inflation, have fuelled anger and contributed to a landslide opposition victory in a February general election.
Early this year, the government shut steel melting units across the country for two weeks and ordered hundreds of textile mills to reduce operations to cope with the power shortage.
In April, textile workers staged violent protests against power cuts that have crippled their mills.
Pakistan's installed capacity is about 19,845 MW, of which about one-third is produced by hydro-electric plants. Much of the rest is generated by thermal stations, fuelled primarily by gas and oil.
But no new capacity has been installed for the past decade despite strong growth and rising demand for power.
Power cuts are likely to worsen over the next few months as the weather heats up and air conditioners are switched on full blast.