A stop is an instruction to trade at market once a level is touched. It controls the decision, not the fill. In a deep book the difference is small; in a thin one it can be large.
Why the thin hours are worse in three ways at once
Spreads are wider, so the fill starts further away. Depth is thinner, so the order walks further through the book. And moves travel further, so more stops trigger together and compete for the same depth.
Those effects compound rather than add, which is why an overnight stop-out can fill meaningfully worse than the same stop in a main session.
The wick problem
Thin conditions produce the sharp, fully retraced spikes described in reading a liquidation wick. A stop inside wick range is taken out by a move that means nothing and reverses within minutes.
That is the most expensive failure available: correct thesis, correct level, removed by a mechanical event.
What follows for placement
Wider stops than a main-session equivalent, sized so the wider stop still leaves an acceptable loss — which usually means a smaller position rather than a tighter stop. That is the trade-off, and tightening the stop to keep the size is the wrong side of it.
And placement away from the obvious cluster levels, since those are where forced flow concentrates. A stop just beyond a round number sits exactly where the liquidations are.
The mark price wrinkle
On a perpetual, your stop executes on the traded price while your liquidation is judged on the mark. Those can differ during a violent move, so the two protections do not trigger on the same number — worth knowing before assuming a stop will always fire first.