In the morning at 9 a.m.; all day, until closing. However, I do not recommend doing this by yourself later in the evening.
Mine am till....
I think it opens from 9am-9pm. If memory serves me well, they extend hours during holidays, probably until 10pm. And as the other reply said, do not wander alone late. Perhaps they'll increase security for the holiday season but still use caution.
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