You don't have to wait for the entire update process to finish before you can preview your work. Use the draft and make-page actions to create an intermediate preview of your work.
Create the new entry or article with draft.
nb draft preview.txt
Create the preview with make-page.
nb make-page preview.txt preview.html
When you're satisfied with the preview, initiate the update sequence.
for an entry:
nb file preview.txt add entry
for an article (from the articles directory):
nb query main update