I read a lot of crime fiction, the book I am currently reading is 'Love you Dead', one of the Roy Grace series set in Brighton, UK by Peter James.
Apparently, according to the story, an 'Arduino relay' makes a really reliable timer for a bomb. You can buy an 'Arduino relay' from an electrical supplies place. 'Arduino relays' are really easy to program, although exactly what you program them with is not clear.
It's a shame Peter James wrote this, much of the policing stuff he puts in his books seems well researched, and certainly I recognise a lot of the parts of Brighton he mentions, having visited them myself.