Ok. Lets try this from another angle: you have sunshine from 7am to noon. Lets ignore seasons. Your tank gets that sunshine. Period. If you do not move the tank or get better blinds or cover the tank with a blanket, it gets the sunshine. Assume you go all green

and never turn on your aquarium lights. If you want a healthy tank (good plant growth. no algae, etc), the plants need proportional supply of food / building material to keep up with the amount of energy (sunlight) they receive. So, that's your step number one. If your tap water + fish waste + leftover fish food + decaying plant matter + gas exchange provide more food then the plants can absorb (normally unlikely) you probably want to lower it. How? More water changes, RO, feed less, add more plants, etc etc.
On the other end, if your plants do not have enough food (more likely) you want to supplement it externally, I.e. co2 and appropriate ferts.
In any case, good tank management: plant load, fish load, cleaning, etc are given tasks.
So, once you 'balance' the tank with existing sunlight you are all set and happy and can enjoy it when the sun shines through and you are home.
But we have a problem: the sunshine and your presence at home do not overlap. OR the amount of sunshine is not enough to sustain decent plant growth.
This is where the step number 2 comes to the rescue. Namely, we turn the lights on. If you have to supplement the tank to handle the sunshine, then you need to supplement proportionally more to account for each minute the lights are on? How much? That depends on the amount and 'quality' of energy your specific lights add to the equation.
Am I making any sense?
Back to practical: 7 to noon = ~ 5 hours of unqualified photo period (we don't know how much sunshine gets filtered, how much of the tank is in the light, etc). Say you increase the total photo period to 9 hours: lights on at 4 pm, off at 8 pm. Watch the tank for 2 - 4 weeks add / subtract co2 + ferts + flow + surface agitation until fish and plants are fine and no / minimal algae. Then add another hour (lights off at 9 pm), repeat the process above. Repeat as sensible.
My $0.05
v3