That's not the parameter you're looking for. That time is in seconds since the epoch, and is the time the alarm was recorded at. It is recorded when the alarm is created, and it does not change afterwards.
It is used to that if traps are forwarded to other systems, it can be used to show the time the fault was detected, as opposed to the time the alarm was forwarded.
I think I know what you're trying to achieve - delayed email alerting - and there's no easy way within IMC to do it. You need to either forward the alerts to some other system that can handle delayed alerting (e.g. ScienceLogic, xMatters, PagerDuty), or you can write your own scripts to do it.
I wrote a script that does delayed email alerting by querying the DB, but it's a bit ugly. The better way is to query the eAPI, assuming you have the license.