Try the below code:
SELECT CAST(DATEDIFF(HOUR, '16:26:46:235', '16:26:50:924') AS VARCHAR)
+ ':' + CAST(DATEDIFF(MINUTE, '16:26:46:235', '16:26:50:924') AS VARCHAR)
+ ':' + CAST(DATEDIFF(SECOND, '16:26:46:235', '16:26:50:924') AS VARCHAR)
+ ':' + CAST(DATEDIFF(MILLISECOND, '16:26:46:235', '16:26:50:924') AS VARCHAR)
This should give you what you are looking for.