Let's say a small group of people, 10-15 or so, were going to travel back in time to the mid-1970s, the time of the first personal computers. They can have experienced software developers and hardware engineers in the group, and can each bring one laptop or tablet computer with them, which (given today's limitations) can hold an arbitrary amount of technical data.
Knowledge is not a problem, but the technological installed base is. The technology to create modern computers does not exist back then, and as the development of such technology is an inherently iterative process, the technology to create the technology to create modern computers also does not exist.
Assuming our group has specifications, and a limited amount of hardware to reverse-engineer, but very little in the way of money, how long would it take them to be able to mass-produce modern (2010s-level) computers?