Three clocks are running
There is the business clock (is performance rising, flat or slipping?), the market clock (are buyers active in your sector?) and your own clock (energy, health, family, what you want the next decade to look like).
Owners tend to watch the first two and ignore the third. In practice the personal clock is the one that decides.
Sell from strength, not fatigue
A business sold while still growing attracts more buyers, better structures and fewer awkward questions. A business sold after two tired years attracts bargain hunters.
If you can see the point where you will stop wanting to invest in the business, start the conversation eighteen months before it, not eighteen months after.
Signs the moment has arrived
You have stopped saying yes to projects that would pay back in five years. Reinvestment has quietly slowed. You are managing rather than building. Or simply: you have had a good year and you would be content if it were the last one you ran.
None of those are emergencies. They are just the point where planning beats waiting.