We are still building it. :)
@fazlerocks and I had built a prototype called devmag.io in early 2015 to test our assumption that developers need a friendly & conversational network (as opposed to bug based Q&A). We launched it in Jan 2015 and got good traction. It was very minimal, but the core concept was same as that of Hashnode.
After running devmag.io for around 6 months and gathering initial user base, we decided to go a step further and build Hashnode. It was a complete rewrite. We started in mid-August 2015 and were done with the initial version in early December. So, you can say it took us around 3 months to come up with the initial release.