How long your Seiko watch lume glows depends on a few factors. How well was it charged up by the light source? How old is the watch? And most importantly, how much LumiBrite luminescent material is on the dial?
That is why this question can’t be answered definitively. It really depends on the model.
If you are worried about lume not lasting long enough when the lights are off, then consider a watch with tritium tubes. Tritium will provide a subtle but constant glow.