We are not sure how many of these (little) guys you treat, but this article is germane.
4 hours per day, 5 days per week. It takes time to recannalize (or re create) new (or rejuvenate old) neurological pathways.
"After only two weeks, the children in the experimental group demonstrated a significant increase in locomotor and object control skills and in gross quotient (a composite measure of both skills categories). Participants’ locomotor improvements plateaued between weeks four and eight, and object control skills improved during the first two weeks but demonstrated nonsignificant changes between weeks two and four, four and six, and six and eight. A significant gain in locomotor skills also occurred between weeks four and eight."
...and don't forget about the "neurological windows" we are always talking about. Aggressive, early intervention is indicated
"Early childhood is a sensitive time in development, and motor researchers have an opportunity to improve motor skills very early—even as young as 2 years, said Ketcheson. Early intervention may give children with ASD the ability to play and interact in age-appropriate ways with their peers entering kindergarten. Early intense motor skills instruction within a CPRT framework can be a valuable addition to practitioners’ intervention strategies aimed at improving social success for children with ASD, she said."
Get them up, get them moving!