The main season is May to October, when the Srinagar-Leh road is usually open and daytime weather is manageable. June to September is best for combining Lamayuru with other western Ladakh stops, though summer sun at this altitude is fierce.
The Yuru Kabgyat festival at Lamayuru Monastery usually falls in June or July according to the Tibetan lunar calendar. Dates shift each year, so confirm in Leh before building an itinerary around it.