Wake windows lengthen with age, from roughly 30–60 minutes for a newborn to 3–4 hours near a year. The idea is that babies build up 'sleep pressure' the longer they're awake, so catching them at the right point makes settling easier. The first window of the day is usually the shortest and the last before bed the longest. Treat windows as a rough heads-up for when to watch for tired cues — the cues themselves are far more reliable than the clock.