Pg 538 MtA 20th: "By definition, ritual refers to a practiced sequence of events with a desired end."

Pg 539 MtA 20th: "Some rituals involve brief activity, and others can take hours or even days."

If the ritual itself involves breaks, pauses, or has checkpoints that can be paused and resumed later, then you can wait to complete the ritual in the manner you describe.

The example in the book states creating a summoning circle to commune safely with an angel without your head exploding requires carefully writing protection runes and sigils over a period of time. After writing the sigils, you can pause indefinitely until you're ready to proceed to the next phase. But once you start the incantation, you have to continue until you're finished or you lose the successes for that portion of the spell. You can't hold back that last syllable to invoke the angel on a whim; if you stop the incantation, the "angelic operator" drops your call and you have to start dialing all over again.

This boils down to how your ritual is defined. If you must use a burning sprig of rosemary to light your target's picture on fire while reciting ancient Babylonian, then throw the ashes at them to activate an effect, your storyteller could call for all the successes to be rolled during the burning, then once you collect the ashes the effect is locked and loaded to use when ready without having to "roll the last success".

I can provide a better answer if you explain what you're trying to accomplish it.

Pg 538 MtA 20th: "By definition, ritual refers to a practiced sequence of events with a desired end."

Pg 539 MtA 20th: "Some rituals involve brief activity, and others can take hours or even days."

If the ritual itself involves breaks, pauses, or has checkpoints that can be paused and resumed later, then you can wait to complete the ritual in the manner you describe. So if the ritual is defined as being able to complete it ahead of time and then releasing the effect of the ritual at-will at a later point in time, then you're able to do what you're wanting.

The example in the book states creating a summoning circle to commune safely with an angel without your head exploding requires carefully writing protection runes and sigils over a period of time. After writing the sigils, you can pause indefinitely until you're ready to proceed to the next phase. But once you start the incantation, you have to continue until you're finished or you lose the successes for that portion of the spell. You can't hold back that last syllable to invoke the angel on a whim; if you stop the incantation, the "angelic operator" drops your call and you have to start dialing all over again.

This boils down to how your ritual is defined. If you must use a burning sprig of rosemary to light your target's picture on fire while reciting ancient Babylonian, then throw the ashes at them to activate an effect, your storyteller could call for all the successes to be rolled during the burning, then once you collect the ashes the effect is locked and loaded to use when ready without having to "roll the last success".

The example you brought up in the comments also works this way. You have to program a reality-altering executable. All the rolls and magic happen during the programming part while you're making something like Intelligence + Computers and making an arete roll on top of that. Once the program is finished, the ritual is locked and loaded and ready to use whenever you press the button. No roll should be needed to use the effect (unless the effect itself needs aimed or thrown or whatnot).

I can provide a better answer if you explain what you're trying to accomplish it.