When your making an oral presentation of your biography, it is good to practice to

It's good to practice saying it in front of people, so you don't freeze up when you actually give it.

The sentence needs a descriptor of exactly "what" will happen at gurley and marina. in this case, it is the light at the intersection turning green. in this case, the sentence could be rewritten as "the light at the intersection of gurley and montezuma will turn green exactly three seconds after the light at the intersection of gurley and marina."