I play regularly 45+45 games with a duration between 2-4h. During my opponent's time I normally try to guess their moves or try to understand the position better. Regularly I have the problem that I reach the endgame too tired to calculate deeply and correctly.
On chess.com I read about the idea "think on their time, check on your own".The reason for this: "If you calculate on their time, you have a much bigger tree to calculate through - they prune it for you by making their chosen candidate move" (same link).
Are there more concepts about time management especially during your opponent's time to find a balance between time efficiency and exhaustion? Thanks!