Determining how far away is the next ID

The LEAD function can be used to find the next start_time per ID.

And the ROW_NUMBER function can return a unique sequencial number per ID.

SELECT *
, LEAD(start_time) OVER (PARTITION BY ID ORDER BY start_time) AS next_timestamp
, DATEDIFF(minute, start_time, LEAD(start_time) OVER (PARTITION BY ID ORDER BY start_time)) AS time_diff
, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY start_time) AS entry_order
FROM your_table
ORDER BY start_time

Using LEAD, DATEDIFF and ROW_NUMBER:

SELECT *,
   LEAD(start_time) OVER(PARTITITON BY ID ORDER BY start_time) AS next_timestamp,
   DATEDIFF(seconds, start_time, next_timestamp) SA time_difference,
   ROW_NUMBER() OVER(PARTITITON BY ID ORDER BY start_time) AS entry_order
FROM tab