It depends on a lot of things as far as work is concerned... tank size, the amount of plants, the amount of fast growing plants, how often you trim or don't trim, is CO2 being used, etc.
It's not too time consuming to keep up with my medium light, CO2, 55g tank but the plants are to the point I'm pretty much having to do trimming and even some thinning weekly now. I can do most plant trimming and such during the weekly WC.
But my very high light 220g 100% planted is a different ball game. Sheer size and number of stem plants often takes daily maintenance, more than just adding the ferts and liquid carbon, especially since adding CO2. The plants could overtake the tank in 2 weeks easy. I know, been there, done that, and it's not pretty, nor fun to fix, which can take hours.
Many people don't even want to have to take the time to add ferts and liquid carbon daily so it really boils down to what a person is willing to do or not do. Even 30 seconds is too much for many people. So when you look at the overall picture there is more time required overall the more high tech a planted tank is. Even a 10g high tech planted can quickly get overgrown if it's not being trimmed, thinned, and replanted in no time. How many times have you seen small high tech- high light set ups turn into overgrown jungles because the time wasn't spent for whatever reason not to keep them maintained the way they should be.