Totally agree with Polarbear!
DS had over 2 yrs of VT between 4 and 6 yrs old. He was born with visual deficits that related to hand-eye coordination, fine/gross motor skills, perception, body in space (vestibular), sensory, attention, and some other issues. Before VT, DS barely scribbled, despite 4 yrs of OT and other therapies.
We saw the behavioral optometrist every two weeks and got a series of daily exercises to do specifically designed for DS and his needs. Most of the exercises took 15-20 minutes to do. At the time, we did them after school, I think. However, some days DS didn't want to cooperate and the exercises took considerably longer to do. I admit that the exercises were a slog some days, but we were persistent with them because we wanted DS to write and since we were paying out-of-pocket for it! Still those initial exercises could be very tedious and laborious - hand over hand tracing stuff.
We had huge success with VT over time, but it took 6-8 months before we had the first big breakthrough with VT. Until then, we did wonder at times what to expect.
Before we did VT, we had no idea that DS was eg/pg. We knew DS was bright but not eg/pg. Well, that changed with VT. If we hadn't done VT, I shudder to think about it. DS would be very frustrated, angry, and depressed.
VT really is amazing. It completely changed DS's life and ours. With VT, you're re-wiring the messages between the eyes, brain, and body.
In our situation, DS is now finishing neurofeedback therapy - a year after finishing vision therapy. This seems to reinforce what happened with VT more. Between NFT and VT, it's really amazing!