KB has given examples of how you can say what was intended in that sentence.
As for "long after…", I can't think of any context in which you'd use it preceded by "it is" (present tense).
Here are a few examples of its use:
My grandmother took a job in a local store long after retiring from her career as a teacher.
Long after he [had] left, we still missed him.
Sometimes an ailment recurs long after it was thought to have been cured.