Child Custody during Seperation

My wife and I are seperated but have yet to have a formal seperation agreement done. Is there any bearing on custody later based on the number of nights per week a child stays with a given parent?

For example the child lives with me but my spouse is wanting the child to stay overnight more and more. Will that have an impact on customer later?

Maybe. These situations are very fact specific. The starting point for the court is that both parents are fit, and if the status quo works then the court is likely to order it to continue.