I just spent around thirty minutes trying to figure out when everything in TGH happened, and this is what I settled on.
Jennifer said Star was born on the shortest day of winter which is December 21st. Soo...
December 21st- Star's birthday. (And Morningleaf's!)
March 27th- Starfrost is born
March 29th- Riversun is born and Starfrost taken.
March 30th- the tunnel is finished and Echfrost gives the signal.
April 6th- tornado, battle between Star and Nightwing, Echofrost and Hazelwind and the 140 steeds leave Anok.
Now, I was just guessing when I say this is when it happened, but Starfrost and Riversun were born in the spring two days apart. The day after Riversun was born, the tunnel was finished, and seven days later, Star killed Nightwing. I, of course, don't know the exact date they happened, but these are my guesses.
Another thing, I don't think this makes sense. In the books, correct me if I'm wrong please, it said Star and Morningleaf were born on the shortest day of winter, a month before the other foals. But, if the other foals were born a month after, they would have been born in January, in the winter, when they should have been born in March or April, which are the foaling months, and in the spring. So that doesn't make sense.
Tell me your thoughts!