How long should one scene for a scripted play be?

It can be as long or as short as you like. Some scenes, when they are short, create a dynamic feeling. Other longer scenes can be more consistent and interesting. Do what you think will create the most dynamics. :)

My advice for this is do not rush the scenes. Do not do the minimum and only write a few paragraphs.  You must unfold the story in a timely manner. You can use as many scenes as you need to get the first part of your story across. There is not a specific number of scenes needed for a play. A play needs to be very fluid and easily adaptable for the plot of the story.
Hope this helps, and good luck! <3