Generating random mock data with specific time range

I wanted to generate mock data with the below structure, But Start time and end time interval should be 30 Mins.

  [{
    Id: 1,
    Subject: 'Bob',
    StartTime: new Date(2020, 6, 11, 9, 30),
    EndTime: new Date(2020, 6, 11, 11, 0),
    CategoryColor: '#1aaa55'
  }]

I tried with this generating tool but issue is, time interval is not maintained.

Could you please suggest any alternate approach to achieve this ?