You don't need the time test.
As the delete operator says in its rollout, just adjust its timing settings.
If you want it to delete particles that are 40 frames old in the event, just set timing to "Event Age" and set the "from" spinner to "40". The "to" spinner's default value is "1000", which is fine in your case. That means any particles whose event age is between 40 and 1000 will be deleted. Make sense?
As the delete operator says in its rollout, just adjust its timing settings.
If you want it to delete particles that are 40 frames old in the event, just set timing to "Event Age" and set the "from" spinner to "40". The "to" spinner's default value is "1000", which is fine in your case. That means any particles whose event age is between 40 and 1000 will be deleted. Make sense?