Financially we had a 5 year plan. Then after a year had passed, I'd update it, so it'd be a 5 year plan. Then again the next year. Always a plan for the next 5 years, for several years in a row.
Then suddenly, one year I updated it, and it was only a 4-year plan. FIRE was to happen at year 4. The next year it became a 3-year plan, then a 2-year plan the following year.
Midway through that year, we decided to pull the plug a year early, so we skipped what would have been our last year.
So financially, we weren't quite ready.
But mentally, we were. The wife especially was feeling over work, she felt a little burnt out.
I felt mentally okay with pulling the plug early because I got comfortable with all the ideas for various backup plans, flexibility in spending, earning extra income, going back to work, semi-ER, side gigs, etc. etc.
So we knew "it was time" because we wanted to not work anymore, and got comfortable enough to not worry that the money wasn't quite ready, that it likely would be fine (keep in mind, for example, if you're at an 80% success rate in FIRE, and pull the plug then, instead of at 100%, you may be done "early," but likely the money will work out anyways, just fine).