Not in my experience. If I'm sneaking around a restricted area in a suit, I get no opportunities to duck out of an enemy's LOS before he detects me: It's instant. Unless I've been doing something horribly wrong, but enemies have always immediately opened fire at me the second they looked at my direction.
Unlike absolution where detection is gradual and I get a directional warning and an audio cue.
Unlike absolution where detection is gradual and I get a directional warning and an audio cue.