Oh yes, they aren't planning on simulating anything close to Griffie's entire life. Even the first run will be just the most promising parts and they hope to assemble a 10 minute loop of just the actual decision points behind Griffie's greatest hits.
In terms of subjective experience:
There are two layers to the simulation. The outer layer is a vauge, literally dreamlike, control area that gives the impression of a pleasant forrest without actually having any trees or really any unambiguous physical features except for their bodies and the control board for the inner simulation.
The floating display has hundreds of switches, dials, and menus as well as a view port to the inner simulation. Despite this apparent complexity, Griffie simply needs to decide on a memory or set of memories and tell Inovemena to press go. Everything else is a mix of manual backups, performance tuning, and tools for assembling the eventual loop.
If there is a easy way for them to measure quintessence from completely outside the sim that would be helpful, but Griffie should be able to overlap eir real and outer sim bodies for the purpose of casting by wanting to.
The inner simulation is indistinguishable from reality to the inner Griffie as long as outer Griffie wills that.