Ziferblat, thought to be the capital's first pay-per-minute café, has opened in Old Street, London EC1.
The café is the first UK branch of a Russian chain where "everything is free inside except the time you spend there". The fee for a visit is 3p a minute.
The name Ziferblat comes from the Russian for clock face, and its owners describe it as a "treehouse for grown-ups".
On arrival, guests take an alarm clock from the cupboard and note the time. They are then invited to make their own coffee, help themselves to biscuits and use the facilities, such as Wi-Fi, a selection of books and an antique piano.
Owner Ivan Mitin told the Daily Mail that he hopes the idea will serve as a "social experiment" and added that some customers were even washing up their own dishes.
"Londoners are more prepared for such a concept; they understand the idea instantly," he said. "It's funny to see people queuing here to wash their dishes. It's not obligatory, but it's appreciated.
"They even wash each other's dishes. It's very social. We think of our guests as micro tenants, all sharing the same space."