The later that hail occurs in the season, the more damage it can do to yield. That said, flowering canola can, with enough time, recover from hail that knocks off a large percentage of flowers. Canola will flower for longer to compensate. In serious hail situations where entire flowering branches are knocked off, plants that are still actively flowering can produce new branches. This will set back maturity, but with enough season left, these new branches can produce a decent yield.
As shown in the graph, canola plants have a lot of built-it redundancy when it comes to flower production. This allows it to compensate very well in the case of early flower loss. This is Figure 12 from the Canola Encyclopedia Crop Development section.