I haven't visited for a few months, but last time I was there you didn't need to book, but it is a good idea to turn up early. I think they open at 9:30.
All you need is what's called a newspaper pass, which you pick up at reception. You leave you bags, coat, phone etc in a locker room, find a free machine in the RC research room (up the stairs to the right), and note the desk number. Then go upstairs to the main library room and order the film giving the film reference and your desk number.
The film will be delivered to you at your desk, when its ready.
they are open Mon-Fri and for a while on Saturday morning.
Early records dont contain much details, so it's quite likely that all you will see on that marriage record are the details mentioned on IrishGenealogy.
For full list of the St. Andrew's films in the NLI see :
www.nli.ie/en/parish-register.aspx Shane