If I recall correctly, after the mainnet was delayed for a few days or weeks, the team decided that they won't put dates into the roadmap. And I think it's better that way. I'm a programmer and I know that sometimes you come across some problems that you just couldn't foresee and that causes a delay. And then the community gets angry and so on. It's better if there are no exact dates. Besides, in most roadmaps you can see what will happen in each quarter of a year (Q1 2018, Q2 2018...).