Ritual Caster

Let's leave well enough alone with the durations. I think the book RAW is pretty decent on those.
The Blade Ward or any other Cantrips you think should be converted, maybe those need adjustment and I'll defer to your judgement on that. The 1st level and up, let's let those stand as they are in this department.
That being said, it would make sense to change too, but looking for some opportunities to just keep it simple here and there.

Bro, that Find Familiar casting description is legit occult. First Team All-American Creepy.

+1 Ritual Spell for every +1 INT Mod sounds good. Will let people see a payoff for the Ability Score, which is good.
So extra 1st level spells? Is that right? I think that is best, mainly to control the release of 2nd and higher level spells on a more gradually, story line dependent basis. And again, them casting ANYTHING in this world is a big deal and sets them apart in the very rare category of sorcerer, arcanist, etc.

I think the DC for casting is a great idea. Gives some uncertainty and a lack of total faith in depending on magic, but I feel like it should be some increments easier, more of a sure thing, especially for 1st level spells. At 3rd level, Proficiency +2 then maybe INT 15 (+2 Mod), that's only a +4. Even that guy, I'd like him to feel pretty good about his effort to cast a spell working. His Ritual Caster Feat spend should set him up with a decent capability, with failure as a possibility, but a low percentage especially at the low level spells. And if guys are super squared-away with big INT or something like Expertise, then they should get down to the 5% natural 1 only failure pretty quickly. With this in mind, I think base DC for 1st level spells should be maybe 7 or 8 max. And they go up +1 per level. With INT Mod +5 as max, that will also be theoretical max of spell level. That would give a DC 12 or 13 as the high DCs. I think that's ok, because I think the practical manifestation that we are going for is that a caster who is decent USUALLY has success, but sometimes he blows it because he's just not a full-time student. Meanwhile, the solid caster who is has done the background study in Arcana and has the natural brains RARELY ever botches it.

Casting time reduced by 10% per +1 INT modifier? With percentages you can apply the time reduction across any unit of time.

Thanks :) I like it a lot as well. It just made sense. Rituals in this setting should be dirty and rough, calling upon ancient magic to get the job done.

Agreed, They should usually find success. However, I wouldn't get concrete with Ritual difficulties. You should set them as you create or release them, and set the DC's based upon the nature, power, and level of the spell (e.g., summoning a demon should be in a separate class, or casting a hex spell might be a little more difficult). The idea behind this being that low INT hacks without at least proficiency in Arcane shouldn't be screwing with some things.

You could always set difficulty based on what a talented ritualist should be able to do. So, for example, say you got a 5th level guy with a +10 Arcane, and you have Hex ritual that you want to work most of the time for someone appropriately talented at Ritual Casting at 5th level. Say you want it to succeed 80% of the time, which would mean that their effort should fail on a roll of 1-4. Then you set the DC at 15, so that when they roll a 5 or higher, they succeed (5+10=15).

Just a quick example, but I think having a uniform pattern for Ritual difficulty should be tempered with an analysis of the ritual types and relative power (e.g., if made into Rituals, Tongues should be less DC to cast then Clairovoyance, even though they are both level 3 spells).

Percentage based casting time reduction. Yes. Perfect.

Yeah. OK. Makes sense. No stated increase rate or predictable rating for DCs. Needs to be flexible and contextual to the nature of the spell.

Also, some may even have a chance of not just failure but catastrophic failure, as in backfire or unexpected consequences. The demon summoning should be extra scary as an example, a high stakes roll that everyone is a bit nervous about. No 1st level spells should have any danger though, just ideas for higher level or specially designed spells.

I think the 1st levels could have negative results for failure, just not catastrophic. E.g., temporary blindness, sick feeling (-2 to attacks or checks), etc. There is a tremendous amount of variety you could create for ritual failure.