I trim when a few hit max, then I trim the lot or box. You can get a little jig that goes in brass and check your actual chamber, then you will know if it is longer or shorter than what is listed.
How do you know what 'max length' is? Have you measured it in your chamber?
I determine max length per my chamber & trim all to the longest length I can get them all to. Hopefully(if I planned it right) this ends up within 5-10thou of chamber end after fireforming.
The closer to chamber end, the faster the neck sealing, with lower sooting & ES.