Can osteochondroma cause stress # in a similar location? if so will healing time of the # increase?

Yes and maybe: It really depends on the size and location of the tumor. The tumor itself can fracture, or the bone above or below it can fracture if the tumor causes enough deformity. If the tumor was surgically removed from a weight-bearing bone, there may be a defect in that area which is prone to a stress fracture. Healing time is very individual. Follow your ortho's instructions to heal quickly!