October and November are the best months for Nepal On Bicycle, with clear post-monsoon skies, dry roads, moderate temperatures in the Terai (25-30 C) and cool but manageable conditions on the Daman climb. March and April are the second-best window: warming but not yet hot in the lowlands, clear in the hills and uncrowded.
May can be hot in the Terai (up to 36 C at midday), making the two 150 km stages demanding, though early morning starts reduce the heat exposure. The monsoon (June to September) brings wet roads, landslide risk on the Tribhuvan Highway and high humidity in the plains; most road cyclists avoid these months. December to February are cool to cold at altitude, particularly on the Daman overnight, but clear and manageable for fit riders who pack a warm layer.