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I think 300 hours is just an average number surveyed of study hours by CFAI. The idea is just to say it’s not an easy exam and it requires consistent work.
I don’t think you need to keep track of hours per se, it’s more important that you keep track of your study schedule and stick to it. As you rightly said, quality beats quantity. When you’re in the flow, lots get covered in 1 hour, vice versa.
So I’d go for goals/objectives-based. Map out your available time in the week and review the scope of what you have to study. Set a plan to finish clear, measurable goals each time to study, like X pages, or 1 study session etc.