I started in early season 2015 (season 5). I did hit level thirty about halfway through the season and waited a long time to do my provisionals. I did them at the very end of the season and placed Silver II, then played a few more games, but not enough to get anywhere.
In season 2016 I played a bit early on then I waited awhile to finish my placements. I placed Silver III, climbed to Silver II, then gave up doing ranked. Normal games were more fun.
This season, I finished my placements a bit more than a month ago and I placed into Silver I in Flex 5v5 Queue, Silver III in Flex 3v3 Queue, and Silver II in Solo/Duo. I have done a lot more ranked games than previous seasons, and I've climbed to Gold V in Flex and Silver I in Solo/Duo.
I don't think there's a right time to do ranked. I think you should do it whenever you feel like it.