Tbh, not much.

That being said, spaghetti sauce. Yeah, home made is better, but "doctoring" a jarred sauce gets 95% as good without hours of work. You can't fix the canned shit, but I've not found a jarred sauce that I can't tweak with fresh herbs and some quickly sweated aromatics and end up with something that people love. It also satisfies my picky ass. Now, I will say that fucking ragu is pretty shit overall, and doctoring it only goes so far. But it is still good enough that making sauce from scratch ain't happening.

Edit:

There seems to be a lot of range in spaghetti sauce recipes. It's also important to note that I'm not talking about marinara.

So, the real time involved is split between prep and simmering.

Here's how we do it. Remember this is an american talking here, so don't redirect expect something traditionally Italian. And I'm a southerner that's mostly german and Scots-Irish, so don't expect any new York style stuff lol.

You take your tomatoes, skin them however you prefer. I use a quick dip in boiling water, aka blanching.

You give those peeled tomatoes a rough chop into nice size chunks. Now, the kind of tomato matters for that because something like a roma e isn't gong to need as many chops as a beefsteak. You'd usually be using something like a roma anyway, but if your neighbor drops off a giant bucket of tomatoes, you can only use what you got, you know?

You chop up an onion, maybe two. You mince some garlic, maybe half a bulb if you really like garlic. I love garlic, so I go heavy.

Now, that's your usual start. Most people in my family don't add anything else in the way of veggies. Me? I like to char a couple of red or yellow bell peppers, skin them, and get them in there too. If I'm feeling frisky, I might have zucchini, eggplant, or whatever else cut up and ready to add at the appropriate time too, but that's optional.

You get the onions sweating. While they're starting, you feet your herbs together. Idgaf about fresh vs dried, each has benefits for flavor, you do what you prefer. I do oregano, basil, marjoram, a little thyme, and that's it. I'm simple.

A little black pepper, a little salt (you really don't need much, maybe a teaspoon for a big batch; salt your damn pasta water instead) to taste.

Once the onions are almost ready, I add the peppers since the quick char and steam to peel them tends to get them halfway cooked anyway.

This is around a half hour of work for most people. For me, it's closer to an hour. Yay disability!

Then you add your tomatoes, herbs, and any optional veggies. Bring to boil, reduce to simmer.

After that, it's patience. You're making sure any veggies added are tender, and after that it's cooking things down and letting the flavors develop. And, I promise you, anything under a half hour of simmering isn't going to taste right, and will be super runny. You'll usually have what amounts to chunky tomato water until close to the hour mark. For a big pot (my biggest is 6 quarts, and it starts damn near full when I do it) an hour and a half is bare minimum for the right thickness.

Now, if you're going to jar that up, you're done except for that part, which isn't involved in what I originally said.

If you're going to add meat, you'll want to start browning it off about a half hour ahead of when the thickness will be right. You add the cooked meat in and let it simmer for 15 minutes at minimum. Do yourself a favor and deglaze the pan used with a nice, semisweet red wine, add that to the pot and go at least a half hour after adding it.

Now, exactly how long it needs to simmer is variable because you're dealing with tomatoes, and the water content varies between varieties, time of year, weather conditions, etc. But I've never had a full sized batch take less than an hour and a half counting from the initial bring-to-boil stage.

I dunno, maybe there's time savers I've never thought of. Maybe the folks saying it's a half hour are doing a different version of "from scratch", or whatever. But that's how we do it, and it's pretty much what the typical recipes I've seen online do (I went and checked because I wondered if I was crazy lol), plus or minus some details that don't really change simmer time.

I've had some batches need a full two hours of simmering. And, yeah, you don't have to stand over the pot the whole time, but chances are you'll still be in the kitchen cleaning, keeping an eye on things stirring occasionally, adding any herbs or spices to adjust taste as it goes, etc. So it isn't like you can just pop down to the local pub (or equivalent in your location) and go by time alone. You'll still be in the general vicinity, with the added heat and humidity from cooking.

But that's why I rarely go from scratch. I can pick up a jar of whatever, add some herbs, extra garlic and/or onions, brown any meat and then the deglaze and be done in under an hour from start to finish, including prep. The taste isn't the same, nor is the texture, but it's still yummy.