Spring (March to May) is the best time to visit the Black Rock Desert. Temperatures are mild, the playa may still have water on it from winter rain — making the famous mirror-flat reflections — and the desert wildflowers are out. Autumn (September to November) is the second-best window: the Burning Man crowds have gone, but the days are still warm.
Summer is brutal. Temperatures on the playa regularly exceed 100°F (38°C) and the reflected heat off the white surface is intense. There is no shade. Winter brings cold nights and the possibility of snow, though the playa itself rarely freezes.
Burning Man takes place during the week leading up to and including Labor Day (late August to early September). The event brings around 70,000 people to the playa and transforms Gerlach into a thoroughfare — the town's one main road carries a continuous stream of RVs and vehicles. Accommodation within 100 miles books out entirely. If you want to experience the playa in peace, avoid this window entirely or come in the weeks immediately after, when the event infrastructure is being torn down and the playa is being cleaned.
The land-speed record season has historically been in October, when the playa surface is at its hardest and driest after the summer heat.