It depends on how fast you sew and it you include trims etc. I would say allowing at least an hour to lay out the pattern and cut it would be ample for this step and a good 12 hours to sew the dress, taking into consideration potential need for unpicking and of course pressing time.
When it is a style like this I like to take my time to get it right and usually I use things like mini piping to enhance the collar and sleeves. Allowing this time frame will also allow for any little mistakes concerning the zipper also and if you are learning a new technique.
I think I’m a fairly slow sewer because I allow myself to get distracted due to the times when I sew. But how fast you sew will take into consideration how much time to allow yourself. Once you’ve made one you will generally quicken the pace anyhow.
Hope this helps
Tamara