I was in Japan for 6 weeks in March / April and I'm already missing their sushi. This is my attempt at a salmon nigiri which was nowhere as good as a top sushiya in japan but at the very least conveyence-belt level, definitely much better than most salmon nigiri you find in the UK.
Quite happy with how I cut the skin also !
It's not a weekday lunch for sure, but thinking a bit ahead of time it's not too bad. Also it helps to limit yourself to one type of sushi / fish. I used to do makis + nigiris + tamagoyaki or something and that's always a pain and a half
the way I did it 6pm - wash the rice and let it soak for at least half an hour. I use to think that was unnecessary but in reality the end result for the rice is massively different 6:30pm - put the rice to cook in the rice cooker, take the fish out of the fridge and out of its package to let it breathe.
when the rice is cooked (~7pm), take it out and spread it as thin as possible on a big platter. The finner it is, the faster it will cool down. Then add the seasoning (4 big spoons of vinegar, 1 spoon of sugar, half a spoon of salt, mixed up in a heated pot) and spread it evenly over the rice. Leave the rice next to an open window or next to a fan depending on the weather.
whilst the rice cools down, you can start preparing the fish. I've got to say having a proper sashimi knife I bought in Japan (despite my wife "you don't need any more knives") made it much easier. Also, buying a half back of salmon (like the one on the picture) yields much better salmon than smaller packs in the super market.
Anyway, start by removing the skin, that's like a minute of work, and then cut up slices after slices, perpendicular to the "grain" of the fish (I don't know the terminology, sorry). I takes maybe 20 minutes, and by the time you're done, the rice should be at room temperature.
It's now 7:30pm and you can start assembling your nigiris, doing only a few at a time helping with people appreciating them and not being overwhelmed with the preparation. (I added some proper wasabi in there as well). Having a bowl of water available to make your hands wet really helps.
So to answer the question, that's an hour passive (soaking + rice cooking + fish breathing time), and then maybe 40 minutes of active time (slicing the fish, then assembling it).
For me, who enjoys the process, that's fairly manageable. You can add some frozen gyozas and instant miso soup as well for some variety, and use some of the fish as sashimi as well.