SQL Server 2019

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

IF OBJECT_ID('tempdb..#Results') IS NOT NULL
        Truncate TABLE #Results
    else
        CREATE TABLE #Results
        (
            UserName varchar(20) not null,
            CompletedOn datetime not null
        )      
  
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-23T15:30:00'
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-23T15:31:00'
   --1 min
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-30T12:57:00'      
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-30T13:06:00'
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-30T13:34:00'
   --37 min 
   
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-30 15:31:00'      
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-30 15:33:00'
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-06-30 15:41:00'
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-06 08:41:00'      
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-07 14:29:00'
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-09 15:22:00'      
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-09 16:23:00'
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-21 15:34:00'      
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-21 17:00:00'
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-09 15:22:00'      
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-09 16:23:00'
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-21 15:34:00'      
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-21 17:00:00'
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-21 17:00:00'
   
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-23 06:34:00'      
 
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-23 08:28:00'
   INSERT INTO #Results (UserName, CompletedOn) 
   SELECT 'John B', '2020-07-23 08:28:00'

22 rows affected

UserName	week_num	duration_minutes
John B	1	38
John B	2	10
John B	3	0
John B	5	0