Let it go. A 12-hour day is OK.
Altering the light duration, particularly in the direction you wish to go may lead to hermaphroditism.
Кстати… No matter how much light you give autoflowers, they won’t care. They will automatically flower on their own.
БОЛЕЕ: Почему светодиодные лампы для выращивания растений настолько энергоэффективны?



