Remember glow plugs draw about 11A each, so a relay is recommended, with a relay 15srconds is all you should need, without ~30 Seconds.
I believe the start on key switch and glow plug button/toggle switched places when Universal started installing glow plug relays — the reason is their starter takes >30A startup and 10A sustaining to run just the solenoid. John is correct my GP are on a timer for ~15 seconds every time I turn on the key, the starter solenoid is on a relay to increase voltage to the starter solenoid (cranking noticeably better). And for my sanity alarms are disabled whenever GP are energized.