No, it is not "normal", but I don't believe we are discussing a neurotypical child, are we?
There are 19 possible subtests on the KTEA-3, of which a second grader is eligible to take 18. 6 are required for the core battery. The original estimate of 3.5 hours suggests that the plan was to administer many of the suppolementary subtests. It may be both that your DS was administered more supplementary subtests than you were expecting, and that he took more items than typical to trigger discontinue rules. Consider that, if he did not reach a hard ceiling in both core math subtests, then he completed 80+ items in math computation, and about 70 in math concepts (about three times typical). If the same thing happened in reading comprehension, he answered roughly 3-4 times as many questions as the norm. Between those three subtests, that would be good for easily an additional 1.5-2 hours over expectations.
The KTEA is a high-quality norm-referenced achievement test, with current norms, that should give you a good sense of where your DS's academic skills stand in comparison with a nationally-representative sample of age peers. Although you may receive grade-equivalent information, those should be viewed with extreme caution. The value of norm-referenced testing is in standing versus the peers in the standardization group, which in this case is age-peers (eight-year-olds) and grade-peers (spring second graders), not comparisons with students of vastly different ages or grades.
In combination with the cognitive testing, there should be data that clarifies how his rate of learning and his actual academic acquisition compare to others and to himself.
