Worth adding: fatigue doesn't hit your play evenly. The first thing to go isn't hand reading - it's your willingness to fold. You keep playing your usual ranges, but you stop doing the effortful stuff: checking effective stacks, noticing the nit just 3bet you, taking four more seconds on a river call. Auto-pilot is loose-passive by default.
So you don't feel bad while playing badly. The tell is behavioural: stopped taking notes, opened one more table than planned, insta-called a river - you're already past +EV.
A hand-count limit beats a time limit, too. Time limits get renegotiated at 2am.
