It depends on which route to lowering calories you take.
If you go with a set lower amount of calories that are the same for all days of the week, then just cut them gradually on all days, anywhere from 10 to 20% of all calories is very reasonable. The other way you can go is to lower calories on non training days, and stay the same on training days, maybe with some carbohydrate manipulation, so your overall weekly intake would still be the same as in scenario 1, but you hit a major deficit on non training days. You could also go with intermittent fasting, if your lifestyle allows for it.
A big drop in calories is never immediately and dramatically necessary, unless you want to keep going up and down like crazy
