I don't know if there's a day by day one, but this is better than nothing:

http://www.ultimateafrica.com/travel/Wildebeest_migration.html

This is the latest report (from the 8th of June) from Wild Watch who track the migration: "Now in the Western Corridor of the Serengeti National Park, the mega herds are grazing at Belabela plains, making their way to Musabi and Mbalageti Plains, while the stragglers are still browsing at Seronera in the central Serengeti."

The rains, which push the herds back over the two river crossings and back into Kenya's Masai Mara, have already started so the migration will move towards the river in the next weeks or month, depending on quickly the southern plains get rained out. But it's not an exact science and the best thing to do is to get in touch with one of our Safari Experts who will have several years migration following experience: http://www.worldreviewer.com/holiday/safari-holidays/ for better advice.

If you haven't booked a place on a migration safari for this year already you may be better off waiting for next year.