A few hours a day is probably enough. If it's LED you can probably adjust the color temperature too, so like a warmer light in the evening and a bluer light in the morning, maybe pure white around late morning/early afternoon. Or just get three different bulbs.

Might help for a few hours of high-focus time, then take a break with some dimmer light to reset. Doesn't need to be all day.

Doesn't need to be 30k lumens either. 5k-10k is already insanely bright and should be effective when combined with the right white-balance. Even 500-1000 lumens is plenty bright enough for most purposes. Higher kelvins (like 5k-8k) makes the light more bluish and that's what's most important for treating SAD. Some UV spectrum is helpful for that too as it helps with vitamin D synthesis

If color fidelity is important to your line of work, a bulb with 90-100 CRI is a great idea too.

My desk lamp has a 500 lumen, 5000 kelvin, 90+ CRI bulb and I can't imagine a situation where I would need it to be brighter. I have a similar bulb that's 1100 lumens but it feels like overkill.

We are not the boss of you. Do as you will, including choosing some limited number of hours of exposure.

Why.... wouldn't it be?

Bay light, not bike light. Next time you're in a big box store, look up. If they have round lights, those are the style.