These can range in size from a day (prepare, meet, advise) to a week to assess requirements or investigate a problem and provide a concise written assessment with recommendations to move forward. Sometimes a mini project is requested to scope out the requirements of a project as requirements and implications are not always easy to assess without expert help.
With daily rates ranging from under $1000 to over $2000 for certain specialists, mini projects may be easy to budget and may fall within your direct award rules.