8m awake window or scheduled naps

Our 8 month old has been having 2 naps for about a month now. He usually wakes around 6.30am - 6.45am. We use awake windows for his naps so hes awake around 2.5hrs before nap 1, 3hrs 15m before nap 2 then 3hrs 15m before bed. What signs shows us hes ready to extend awake windows? Hes usually falls asleep independently within 5-10m of being in his cot. Past few days hes woke from his first nap after 45-50m where he used to sleep for a good hr before waking. Hes still tired at this point so we rock him back to sleep for the rest of his nap. Do you follow awake windows with your 8m old or have set nap times regardless of the time they wake? I know every baby is different just wanted to see what people do.