The biographical evidence for both Jobs and Wozniak indicates that Wozniak's version of Breakout (which is NOT the version Atari would release publicly) was likely developed in the first half of 1974.
From the biography of Steve Jobs, we know that in early 1974 Jobs was working at Atari, having been hired in 1973 at the age of 18. We also know that he left Atari in mid-1974 for extended travels in India. Later, in 1975, Jobs would return to work at Atari. This would seem to narrow the possibilities to one of the two timeframes that Jobs worked at Atari - either 1973 through early 1974, or in 1975 after the return from India.
In deciding which of those two periods of Atari employment seem most likely for the 4-day Breakout development, there are three important additional facts:
- The fact that Steve Jobs absconded with the $5,000 bonus paid for Breakout, without telling Wozniak.
- The fact that the compressed 4-day development schedule was invented by Jobs to ensure the work was done ahead of travel plans he was already making.
- The fact that by 1975, Wozniak's and Jobs' biographies indicate they were immersed in Blue Boxes, Homebrew Computer Club, and Woz making progress on the Apple I design.
Number 1 and #2 make it highly suspicious that the Breakout development was intertwined with Jobs' trip to India for the second half of 1974. Together with #3, development of Breakout during Jobs' second stint at Atari seems unlikely.
The reason that Breakout's release was delayed for about two years can be accounted for by the fact that the game was completely redesigned from the Wozniak version and that there was a lawsuit between Fun Games Inc. and Atari throughout 1975 of which Breakout was one part of the legal issues to be resolved.