October through April is when most visitors book, temperatures sit comfortably in the 20s and 30s Celsius, and evenings in the desert are genuinely pleasant rather than something to endure.
May through September gets hot, often well past 40°C by midday, which is exactly why morning and evening safaris exist rather than afternoon ones. The desert at dawn or after 4pm is still very much doable even in peak summer.
December and January bring the coolest evenings, cool enough that a light jacket is worth packing for an overnight safari, when the desert sky is at its clearest for stargazing.
Weekday bookings, particularly Tuesday and Wednesday, tend to be quieter on the dunes than weekends, when local families and longer-staying tourists both tend to book.
If flexibility allows, aim for a weekday morning or evening slot between November and March, that combination covers the best temperatures and the least crowded dunes.