You can put an apprentice on Hold so they do not get notifications for time cards by changing their status.
Go to their page by selecting their name in the Apprentices section.
Click on the Pencil icon just under their profile picture.
A pop-up menu will appear. Select the Apprenticeship category.
Change the status to Hold.
From there, click Save, and you're all set. They'll no longer be prompted to submit their OJT.