“When”, “during”, and “while” all have the same meaning, but they are used in different ways and follow different grammar rules. We use all three of these to say that some action or event happens at the same time as another action or event.

“During which time” is used to talk about an event that happened in a specific time range, while “When” is used to define the specific moment in time when something happened.

When ‘When’ is used to mention about an activity which takes place ‘during a specific period of time’ i.e. to connect two events happening at the same time. When is used to say a longer action which was interrupted by a shorter action. It is also used to denote a specific time age or period of life.