Anytime. I am still fairly new myself so please do not take my word as sure enough evidence. But I did ask my experienced mentor this question and he said exactly what I told yourself
Also I will give an example for you to review in terms of gaps. CNB - Had a gap at 1.30ish which did get filled but still has a gap in the 75cents region still yet to be filled. Just a chart for you to review and learn from.
Also gaps can be formed on any time frame i.e. daily, hourly etc.