You just plant stuff and let it rip, give it a shot, if you don't have land you can always put planters on your porch if you get enough sunlight. Could also always get a cheap LED grow lamp and do it all indoors. Time to harvest depends on what you're growing. Radishes take maybe a month. Except for my radishes, I don't get enough sunlight or something, they grew out all stringy with no root. It was also too hot when I started. I've got this one radish, big fucking leaves, huge, but the root is like my index finger and attached to the ground by a thread

Depends on what you are growing what your climate is like and what your dirt is like. The climate where I am is temperate with really mild winters. (it dipped below 0 maybe twice this winter) so I can have something growing all year round. The dirt here is clay so it is hard to work with. Its heavy and hard and acidic so it is hard for roots to grow through it and extract nutrients from it. So I had to do lots of digging and add lots of biological matter (goat and chicken shit, compost, hay, weeds) to make it more fluffy and lime to make it less acidic. It'll take a couple more years for this to be its best. Other gardens I have had the dirt was practically perfect to start with or was already used so it just needed a little boost.

Our potato patch will probably yield around 100Kg I put probably 20 hrs into prepping the soil and my partner and I put in another 5 or so hours planting this season. I'll probably put in another couple hours weeding, mulching and building up the potato mounds and then harvest in like 3-4 months which will also take a few hours of digging. Potatoes are really easy to grow.

We'll also be growing beets, corn, celery, carrots, parsnip, peas, peppers, pumpkins and tomatoes. but they aren't interesting at the moment as they are just a flat spot of dirt and little green sprouts in punnets. We also have a herb garden and have put in a few berries this season. I'd say if I was paid minimum wage+50% for my work it would cover most of the regular stuff in supermarket but not the more expensive things like peppers and raspberries and the quality of home grown is streets ahead.

Occasionally you totally bork things and end up with nothing to show for your work. Last winter our broccoli got eaten by birds and Possums and we got like 5 handfuls of tiny florets. It can be super disheartening but you push through and do better each season.

Gardening is only particularly work intensive when you're getting everything in the ground and fertilized. You could always set up drip feeders and then it's just weeding.