I would have separated this, at the moment I see the first root tip pushing the plastic. The aftercare is what makes it then. It has rooted. So protect it for a bit so the roots can grow out. This layer is well and beyond the doubt-to-separate-stage in my view.
When taking those pictures I called my wife to show her my success. First time with maples, felt happy you know...
And she said with a cold face "You haven't separated it yet so ???"
She is in no way knowledgeable about stuff I do in my garden though.
How I hate it when she is right about my stuff....