When a film goes into production, everyone knows the story line but scenes are shot according to availability and location. The editor puts it all together in sequence afterward.
As a story writer you know the story. You’ve done your character backgrounds, research, and juggled your scenes around to create a story line with beginning, middle, and end. You know your eight sequences. You have a story outline.
The same process works for writing. You may write any part of the story at any time. You do not need to write in a linear mode starting at the beginning and working to the end. Many writers work on the climax scene first so they know that every scene they write aims toward the ending.
Writing, like story telling, comes in many moods. You may wake one morning with the perfect third conflict in a series of six ascending conflicts in your head. You don’t have to wait until you have written everything that comes before. Write the scene while it is fresh in your head.
Remember that this is a first draft. You will work on transitions and gaps when you review your first draft. For now, you want to fill in all the pieces of your story. The order of when you write the scenes does not matter.