It depends on whether you find one you like and that fits or not. If you do, good to go out he door. If not? Shipping with them can take a long time. Also if you find one but need alterations they generally want 8 weeks advance notice.
We left with a bridal gown on the day of appointment. We didn't need alterations.
I got a dress that fit perfectly and left with it that day.
My mother left with her dress that day, with an appointment to get her alterations done at a later date (she's very short and the dress was very long lol)
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