Internet surfers are advised to become nocturnal as 4am is the time when average speeds are at their fastest, whereas 9pm is the slowest time.
Price comparison service uSwitch conducted more than 2.3m speed tests between July 2012 and January 20, 2013, covering 50 of the most densely populated UK cities.
It found that broadband speeds in urban areas drop by over a quarter (28%) in the evening time compared with the early hours, with average speeds of 14.83Mbps, but dropping to 10.72Mbps at 9pm.
Birmingham and Middlesbrough enjoy the fastest evening surfing, with speeds of 12.88Mbps and 12.87Mbps respectively. By contrast, consumers in Aberdeen and Swansea get just 6.08Mpbs and 6.99Mbps respectively.
But the fastest time to surf the internet in the UK's biggest towns and cities is 4am, when the average download speed is 14.83Mbps.
Dudley gets a superfast 31.81Mbps broadband service at 4am, but that drops by 60% to 12.62Mbps by 9pm.
Stoke-on-Trent residents see the most consistent broadband speeds throughout the day, with speeds fluctuating by just 0.7% when comparing rates taken at 4am and 9pm.
uSwitch said that the difference in broadband speeds during peak and off-peak times was "most significant" in heavily built up locations, due to a "greater demand on services".
Julia Stent, telecoms expert at uSwitch.com, said the study results show the "incredible strain" that is placed on broadband networks when everyone logs on at the same time, particularly in cities.
"The big rise in streaming and downloading - be that films for our tablets, or games for our smartphones - means that striving to deliver consistent speeds will be a long, hard slog for broadband providers," she said.
"It certainly explains why some people may never actually feel like their connection is as fast as the one promised by providers when they signed. The obvious solution of setting your alarm at 4am to use the internet is far from practical.
"Instead, run an online speed test at home to check that you are getting the best possible service available in your area. If you think you could do better, consider shopping around for a new deal."