The family had made a long journey before it is placed on the field. Bumblebees experienced stress during transportation, which can affect their ability. However, this is quite rare and normally the bumblebee family would adapt in 3-5 days. In addition, after the transportation, some supply of pollen still remains in the hive upon arrival, and this may also be the reason why bumblebees do not leave the hive.
If you are using bumblebees for pollination of plants in a closed ground, it is important that that greenhouse has good climate conditions for collecting quality pollen (not just for temperature and humidity, but also enough water supply for the plants, as this affects how attractive the flower pollen is for bumblebees). If bumblebees find pollen unattractive, then they will have less incentive to fly to flowers.
It is recommended to open the hives early in the morning. Prior to this, they must remain in the closed position for a minimum of 2 hours.