Hello JimW23,
I am so sorry that you and your wife are in this painful situation. I don't think there's ever a "good" or "better" time for a child's parents to get divorced. However, there is substantial research indicating that, overall, children are healthier in the long-term when two unhappy parents divorce rather than staying together "for the children's sake."
I think what could make a difference to your child's response is not when the divorce occurs but how. By that I mean, thoughtful discussions from you and your wife with your child...based on research-recommended communication tips. For example, emphasizing that the divorce was not caused or triggered by your child in any way (children tend to assume that). And by proceeding with the divorce process with full responsibility on both sides (you and your wife) that you will make it as peaceful as possible and not go to war with each other. People often assume a peaceful divorce at the beginning but the stress and confusion often trigger some very challenging behaviors and interactions. Each of you respecting your child's relationship with the other parent and not trying to influence it in any way could be invaluable. Basically making peace, respect, and healthy boundaries the top priorities for all three of you.
Personally, I think the sooner we can live our most authentic lives, the better for ourselves and our loved ones. You mentioned that you are not in a high-conflict marriage. I'm not exactly sure what you mean by that. It is certainly good if you two aren't openly fighting all the time. That said, when a husband and wife live together and don't actually want to be...well your child very well could be picking up on some level of tension or unhappiness already. So I don't think delaying the inevitable would necessarily be helpful.
Would you or your wife consider talking with a therapist? They have done a lot of research and know the most helpful ways to communicate the end of a marriage to a child. As I said, I believe the how is more important than the when.
These of course are just my thoughts from a place of care and regard for all three of you. You may not agree.
Peace and hope to you, your wife, and your child.