Really depends on the venue. A friend did her own. A few of us helped make them the day before and then she stored them somewhere cool overnight (I.e. garage or in her case in a barn at the venue) and a family member went to the venue in the morning and put them on the tables, we had laid them up the night before. When I got married a florist did them and delivered to the venue on morning of wedding then the caterers I used put them out when they laid up tables. I did a simple diagram of how I wanted table to look, what order name places were to go in etc.
I want to make my own as I want something simple just a long vase with some long calla lillies in. Has anyone done this? If so did you then have to set them up on the table or do the venue do it for you?