The standard practice in Mahāsī Yeikthā is 1 hour walking, 1 hour sitting.
Walk first, then sit. If you cannot sit for a full hour, you can probably walk for a full hour without difficulty. So walk, then sit as long as you can. When it gets too painful, change your posture once, but not more than once, then get up and walk again. If you feel sleepy, get up and walk. If the legs feel stiff after walking for a full hour, you're doing it right. The Benefits of Walking Meditation
• Walking Meditation