Grant award Dates (US)
There's no fixed timeline. For example, the National Science Foundation has deadlines for proposal submission that are scattered around the year, and once a proposal has been submitted, it may take the NSF 3-9 months to decide. There are also numerous other funding agencies.

In other words, the only way for you to find out when that date may be is to communicate with the professor. He may have an idea when that may be, but the NSF doesn't set a fixed date when they will announce their grants -- that email may come on a random day and a random time.