A 7-week-old infant was admitted with moderate bronchiolitis during the winter season. He required short-term supplemental oxygen on the paediatric ward but did not need HFNC or CPAP.

Over the last several hours, his clinical condition has improved. He is feeding adequately, has reduced work of breathing, and remains alert.

You are preparing for discharge from the Emergency Department observation area. His oxygen saturations in room air are now stable at 91%, including during a period of undisturbed sleep.

The paediatric registrar asks how long oxygen saturations should be maintained at or above this level in room air before it is safe to discharge him home.

For a child aged 6 weeks and over, what is the minimum recommended observation period?