Hi there, Cal-mag will not do anything.Your plant is still have a lot of green leaves and also most of the cal-mag products have Nitrogen in it.So you might not want to add more Nitrogen at this late flowering stage.At this stage, some people will use booster like overdrive to fatten the bud and then flush and harvest.It depends on your taste.For me, I would wait for 5~10% amber and then flush and harvest.Happy growing... ✌️