The reason is that the exit polls until 7 pm included only those voting by 5 pm. When the polls closed, it took about 30 mins to include those who voted between 5 and 7 pm and the projected voting percentages were adjusted. CBS had Trump’s percentage at 32% based on the 5 pm exit polls and changed it to a projected 30% based on those who voted until the polls closed at 7 pm.
Good info, thanks.