It can be difficult to know how to address a time management issue if you have a direct report. There are ways that you, as their manager, can help. Before you give a harsh feedback, consider yourself. You can assess where you have contributed to the problem by identifying the emotions you are feeling and why. Then, communicate your needs to your direct report in a calm manner. Help them set goals, prioritize work, and so on. It's important to celebrate progress at the beginning. If it looks like they need it, consider getting support from a coach.
The tell-tale signs are tasks done late, or forgotten. Tardiness at meetings. There was no response to e-mails or replies at odd times. There is more explanation of why items aren't finished.