Unlike most earlier Final Fantasy games, there are no limit breaks within Final Fantasy XV.
This generally takes about 10 seconds, although if Noctis drops into danger you will drop out of Armiger mode entirely, thankfully retaining what remains on your Armiger gauge. Once you've triggered Armiger mode, the gauge will deplete until it empties. VPN Deals: Lifetime license for $16, monthly plans at $1 & more