I think most conditions have an exponentially increasing risk.
In a 10 minute line (or ride) the risk of an issue is very low, say 5%.
In a 20 minute line it’s still relatively low, but doubles to say a 10% chance of an issue.
By 30 minutes you’re now doubled again to a 20% risk, at 40 minutes it’s a 40% risk, at 50 minutes you’re now at 80% risk, at an hour it’s essentially guaranteed an issue will occur.
There’s a risk in even the shortest line (or ride) but it’s very unlikely, it become’s far more likely as more time in that situation occurs.