OK so...!!!
I had a play around with CASTing and some string functions:
I couldn't get the SUBSTRING function to work, so I used LEFT and RIGHT together instead to extract the timestamp. Note that this therefore does not take any timezones into account - so I'm guessing (???) that it will be in UTC.
Hopefully you can see where I was going, and therefore just add the WHERE clauses and then test it out.
SELECT
CAST (LEFT(created_time,10) || ' ' || RIGHT(LEFT(created_time,19),8) AS TIMESTAMP) AS __time,
task_id,
status
FROM sys.tasks
WHERE CAST (LEFT(created_time,10) || ' ' || RIGHT(LEFT(created_time,19),8) AS TIMESTAMP) > TIMESTAMPADD(HOUR, -2, CURRENT_TIMESTAMP)