Time

TimePlugin inserts a Time resource and ticks it every frame on SystemStage::PreUpdate:

app.add_plugin(TimePlugin)

fn move_player(time: Read<Time>, mut pos: Write<Position>) {
    pos.0 += velocity * time.delta_seconds();
}

• delta()/delta_seconds() — time since the previous tick.
• elapsed()/elapsed_seconds() — total time since the app started.
• fps() — 1.0 / delta_seconds(), or 0.0 on the very first tick.

GraphicsPlugin does not add TimePlugin for you — add it explicitly if you need Time.