Is it possible to walk into the memorial after closing? I was interested in photographing it in the evening.

If you want pictures with no one there, I would suggest you go there when it first opens, early in the morning. Be at the gate first thing.

Yes. I visited the Memorial late in the evening.

The memorial is always accessible to foot traffic but the gate to the memorial drive has certain hours, meaning that the restrooms and parking lot are closed after those hours.