Asr Prayer’s time starts immediately after completing Dhuhr Prayers, but if you want to separate between Dhuhr and Asr, then when the shadow of an item reaches two sevenths of it.
Isha prayer can be performed after performing Maghrib Prayer and it’s Nawafil but if you want to separate between Maghrib and Ish, then after the end of reddishness on the west.
Wassalam.