How to get novice engineers up to speed without wasting time

Fresh engineers are usually not of much use in design work. If you involve them too early, they will mess things up, ask too many questions and waste everyone's time. The best strategy is to assign them improvement of documentation and testing of an existing system. Since they don't know much, any difficulty they have is an opportunity to improve documentation and procedures. That way they can acclimate to the work environment and be useful from day one.

Another important point is to get frequent feedback (e.g. with daily Scrum meetings) because they will retain only 50% of what they have been told and veer off course pretty quickly if not course corrected. Ask them to log in daily comments to the issue assigned to them in the issue tracking system (e.g. Jira).