Should I harvest earlier ? Will this mag def affect on the quality of my plant ?

Yes, it can make it through. it likely has some negative impact, but you'll still have a hefty harvset if all other things are fairly nominal. if adding it isn't stopping it, it may not be the cause. many things cause calcium and mg deficiencies. pH and an overabundance of other elements will do this. check pH and review what you put into your substrate. do the math on the ppm's of what you consistently add.. if you have the meter, check runoff of water-only irrgation for TDS. If you find there's plenty of magnesium available, you know it isn't a deficiency. p and k toxicities can cause it. Think there's at least another too.

I don't think they look that bad at all, the nutrients are traveling from your leaves to the buds, so any kind of nutrient now won't heal the leaves and might only stop a little being worse. I would recommend keeping with your original planned weeks, and keep an eye on trichomes to be more exact picking the harvest date.