With larger tanks that are heavily fed, there is more of a "nutrient sink" available. Also, the fact that you were already running a scrubber on the tank means a brand new screen is more likely to start up faster.
I think that in your specific case here, you can extend hours as munch as you want, there's no signs of potential photosaturation here, the nutrient sink concept helps you avoid that as well. You can probably bump up intensity as well.
So I assume 8pm to 12pm means 8pm-noon, i.e. 16 hours/day? Go to 20, bump intensity to 4 o'clock. That's assuming that you have measurable nutrients, or you are feeding a lot