It took three months to go from inception to private beta. We used an invite only system to introduce artificial scarcity and drive buzz on Twitter (each new signup got five invites to use). After six months we launched to the public and started charging for private repos. Because we had such a great beta period, we converted a large number of users that day and were making money immediately! For the next several months we put every dollar that we made into the company bank account and let it accrue.
One year after inception I was faced with a choice: take a full time position at Microsoft (Powerset had been acquired) or quit and go full time at GitHub. We were making enough money at GitHub to pay low salaries for the three cofounders and we decided to Hire Scott Chacon at the same time. So we went from zero to four full time salaries in one day, a year after starting it on the side.
Over the next six months we incrementally raised salaries for everyone as we hit specific revenue goals. So about 18 months after inception we were making decent salaries. We also hired Tekkub to do full time tech support in this timeframe. Our next hire was Melissa, our office manager a few months later.
As far as revenue at these milestones, we were always profitable. We only hired when we had the money to do so. For the first 18 months we didn't carry much balance in the bank account. We used it to hire great people.
Being a subscription service means that recurring revenue is extremely predictable. We've never had a month where revenue has dropped, and we can predict the increase in monthly revenue quite accurately as well. Growth has been surprisingly smooth (not spikey).
We now make money from GitHub.com, GitHub FI, Training, the Job Board, and merchandise.