Add a stat to the player that affect the duration of the ritual, such as the "ritualDurationMultiplier" server config, but instead of being global it would be for each player individually

I think this is a good idea, but I think to implement it a refactor of the rituals is needed.
Currently the golden bowl stores the ritual recipe, and derives the time from the ritual recipe * config value.

I am not sure if we still store the ritual player (now that rituals can run without a player).
For a satisfying result that also allows automation, we may have to use the player that placed the bowl.

One thing that may be problematic there is how to handle the situation if the player is offline ( I don't think his stat can be accessed then ).

One question regarding stats: Is that something that minecraft/neoforge provide? Or would that be like a data attachment to the player and we have to add commands and interfaces for mods?

The golden bowl can store the value of the last player who interacted (placing it or starting a ritual), and use that stored value, thus solving the problem of offline players and which value to use in automations.

I haven't checked how this is done technically yet.

I am on board with that. Before we get started on that we should figure out how stats work and/or what the exact use case is so we can make sure it works.

Is it something for other mods to interact with?
Or a stat that is intended to be levelled up by the player somehow?
...

Instead of a stat, why not a necklate/ curio item, that speeds up the rituals I'm proportion to a charge you add to it?
Like time in a bottle, but just for rituals. Have so that when a player wearing that item activates the ritual, the time for that ritual speeds up

The principle is that the use of items (curios, tools, maybe potions) can change this statistic (similar to Ars Nouveau trinkets to increase mana and mana regen, or Apotheosis with its gems that increase attributes)

It would be interesting if mods that add a leveling system could modify the stats without requiring items.

Another ideia (that I started testing)

Upgrade the golden sacrificial bowl to reduce the time (halving? afrit tier?)

but this caused the modonomicon to crash when trying to view both using tag

That does sound like a valid idea!