Increase Siri home button press time
I have a habit of holding the home button for a few moments while lost in thought and exiting my current app

There's no setting and no access to any of the iOS files (unless you jailbreak) that changes the duration of the hold button press to activate Siri.
Unfortunately, it will be a habit that you're going to have to change/break. After all, the &quot;long press&quot; required to activate Siri is only 1.5 seconds.    The other option will be to change your workflow to either

use &quot;Hey Siri&quot;
use headphones and activate Siri with that button.