Its not correct.You should not be looking for the nimitta when your practicing jhana.
You should not be looking for anything or doing anything besides focusing on the meditation object.
To practice Jhana means only focusing on one thing and one thing only until Jhana states form.
You are basically doing ONE THING.For 1 hour,2 hours,5 hours,10 hours...etc---focusing on your meditation object----
If you even for a milli second have time to do other things,such as look for a nimitta or think about nimitta Concentration Weakens.
Nimitta appearing directly correlates with how much attention you place on the meditation object.
so while meditating don't focus on the breath while looking for nimitta,while anticipating a light,while...Drop these whiles.
As long as these whiles exist concentration weakens.Weak concentration cannot sustain a stable nimitta.
By the time the nimitta arises you will be GLUED,i mean GLUED DEAD to your object of meditation.Its like being bolted.Its not a state where you can easily shift or move around.You don't have to go looking for the nimitta,it will come to you.