Doesn't work that way. Tesla makes a best efforts to deliver in time to qualify for rebates, but there are no guarantees.
Sometimes they have difficulty getting a specific configuration delivered in time, and will offer different configurations or different colors to those who are flexible and willing to take a 2nd choice to get delivery in time. Sometimes they will even offer a car with a more expensive color or upgraded wheels at the previously agreed pricing.
Website may predict delivery in June, but shipping to the East coast can sometimes contribute to the delay.
They work their butts off, trying to get everyone their cars by the cut off, but for some it will not make the cut.