During the dinosaurs time 100-200 million years ago there were giant insects like 1 meter long. An example is here. One of the theories why they could grow this big is that oxygen level was much higher than now. Now we have like 20% oxygen in the air and that time it was 30 or 40.

The question:

If I make a tank/aquarium with 40% oxygen and all the equipment to make this oxygen concentration constant. I put there modern insects, dragon fly, worms, slugs, etc. Will they grow to much bigger size than normal from the 1-2 generations, or I will need to have 100 or 1000 generations before they will be bigger?