Even if it takes a year for them to identify for the GT program, it's important that the teacher knows the capabilities of the children they're teaching, especially if the child is advanced. What often times happens if you take the "Wait and see" approach is the child doesn't get appropriately challenged and quickly becomes bored...of course this puts a sour taste in their mouths out of the starting block, not the way your want to see your child think about education.
As others have already expressed, better to be "That parent" than for your child to be negative about school because they're bored and unmotivated. It doesn't take a GT program to challenge a child, just a parent and a teacher willing to work together to meet the child's needs and go the extra mile to do so. That's true even after a child is in the GT program. A child usually spends the mass majority of their time in the regular class room anyway, a few hours a week of GT time isn't going to change their need to be challenged on a daily basis. A strong relationship and good communication both ways with the regular class room teacher out of the blocks is what I've found to be a good start.
