Really depends on how high you aim.
My first NSFW game had about 4000 words and a single girl, so I was able to make it in like 3 weeks (although the text already existed before that).
For HHR, I've been tweaking character designs and story details for several months in advance, then once I started properly, making version 0.1 took about 2 months, and 0.2 roughly another 1.5 months, and some people say it still feels like a demo, so...