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A) How much Ca / Mg does it have along with that N?
B) What ppm of Ca / Mg are you aiming for in your overall feed?
C) What's the total N from everything else in your feed?
Plants still need some N during flowering - otherwise they pull N from older growth. That's not a problem during flowering unless it gets too excessive. Feed schedules usually reduce N at the start of flowering, but don't completely eliminate it until the last week or two. That's usually a combination of "why waste N at this point?" and "maybe it'll help give us a jumpstart on curing".
As long as your schedule is reducing N in the rest of the feed, 4% N in your cal mag shouldn't be an issue - just keep an eye out for toxicity symptoms.
As far as using less, most cannabis cal-mags range from 0% - 2% N, but also range from 2% - 5% in Ca, with Ca:Mg in a ratio of 4:1 or 3:1. Unless the cal mag you're using is part of an overall vendor feed schedule, I wouldn't go by the directions on the bottle alone - I'd find another source.
Typically, you want to add Ca/Mg based on the level of K in your feed in order to prevent antagonisms. This article from researchers at NC State recommend using a 4:2:1 ratio of K:Ca:Mg. They recommend targeting 200 ppm K / 100 ppm Ca / 50 ppm Mg based on levels used for poinsettias until there's better research for cannabis. (Note that it's tough to hit that ratio exactly, since commercial cal-mags are already outside that ratio.)