Actually, there is a constitutional requirement. Article II Section Three: He shall from time to time give to the Congress information of the state of the union, and recommend to their consideration such measures as he shall judge necessary and expedient.
As you can see, there is no set time it has to be done, just "from time to time" which has traditionally been annual. You are correct that it is usually done after the first year in office.
Actually, there is a constitutional requirement. Article II Section Three: He shall from time to time give to the Congress information of the state of the union, and recommend to their consideration such measures as he shall judge necessary and expedient.
As you can see, there is no set time it has to be done, just "from time to time" which has traditionally been annual. You are correct that it is usually done after the first year in office.