What speed adjustment is legally mandated for commercial passenger coaches operating during nighttime hours (22:00 to 06:00)?

1. Operating speed must be reduced by at least 20% compared to the daytime statutory speed limit for that road section
2. Operating speed may be increased by 20% due to lighter traffic volume
3. Speed must remain identical to daytime limits under all conditions
4. Speed must be reduced to exactly 10 km/h on all roads