As long as you want within the amount of your monthly quota! The length of each brief determines how many requests you can make and the time it will take the writer to complete. There is a minimum requirement of 300 and as high up to your remaining words of the month.
Do keep in mind that if you exceed your monthly word quota, you will be billed overage rates for those briefs that are submitted after going over the monthly amount.
If you're looking for multiple pieces to be completed, our recommendation is to submit requests separately so they can be done in parallel by our writers and delivered back to you faster.
You can always check what your word limit is listed at the bottom left of your account profile.