For laptops especially you have 2 yearly windows that you really want refreshed models available for. The first is back to school from late July to early September. The next is the holiday window from mid November or so through Christmas. Based only on that tweet, it seems like Tigerlake will officially launch in the middle of the year, but not in time to make the back to school window in terms of volume that OEMs want.
Icelake from last year is a good example, I mean they have launched on August 1. The market impact is very low initially after a mobile launch, it can take a couple of months. Sometimes 1 month and sometimes 3-4 months. However it is obvious Tigerlake is in much better shape than Icelake last year. Intel promises 50 design wins for the holiday season which is 43% higher than Icelake last year.