So for the first watch, Q posted it on 1/5/19. It turned out that it was signifying the date 3/15/19.
That's a 2 month and 10 day difference.
Well the current marker 1 was posted 3/27/19. What is 2 months and 10 days from 3/27/19?
5/17/19
And to follow the pattern, marker 2 will be the time of 3:05pm.