The development of Git began on 3 April 2005. Torvalds announced the project on 6 April; it became self-hosting as of 7 April. The first merge of multiple branches took place on 18 April. Torvalds achieved his performance goals; on 29 April, the nascent Git was benchmarked recording patches to the Linux kernel tree at the rate of 6.7 patches per second. On 16 June, Git managed the kernel 2.6.12 release.
https://en.wikipedia.org/wiki/Git#History
Hogy a nevezetes április harmadika előtt mennyire volt meg a koncepció, nem tudom.