The timers - in everyday use - were particularly attractive to bomb conspirators as they could work on a rechargeable battery alone for up to 100 hours.
Nigel Sweeney, for the prosecution, said: "By using the features of this otherwise perfectly innocent timer, a domestic device can be converted into a long-delay device for use in bombs. You can engineer a delay of up to 100 hours - the length of battery life from the moment you have unplugged the timer from the mains."
It meant bombers would have longer to reach their target, attach the device to explosive "and get a long, long way away before it explodes".
Thirty-seven sophisticated devices - using the timers - were allegedly found at a house in Peckham, after police raided several addresses in south London in July last year. Once attached to detonators and Semtex high explosive, they could have helped cause powerful blasts, the court has heard.
They were designed for use in a plot to blitz electricity sub-stations owned by the National Grid Group. But the conspiracy was foiled by a joint police and security services operation, Mr Sweeney told the jury. Seven members of an IRA active service unit were in London within months of the ceasefire ending. An eighth man was to provide the group with support and find premises in the Birmingham area - where a lorry could be secretly unloaded.
Gerard Hanratty, 38, Martin Murphy, 36, Donald Gannon, 34, Patrick Martin, 35, Robert Morrow, 37, Francis Rafferty, 45, John Crawley, 39, and Clive Brampton, 36, all deny conspiring between 1 January and 16 July last year to cause explosions likely to endanger life or cause serious injury to property.
The trial continues.Reuse content