When you say "I don't have time," it can give the impression that you are overwhelmed or falling behind schedule. This can create confusion regarding when the task will be completed and may cause stress.
Instead of using that phrase, a more effective alternative is to say, "This is not my priority at the moment." By saying this, you communicate that you are currently occupied with another task and giving it your full attention. This statement conveys enthusiasm to finish the current job efficiently and possibly take on the next task as soon as possible.
Using this approach provides a detailed description of your situation. It lets others know that you are actively engaged in your work and demonstrates your commitment to completing the task at hand. Additionally, it sets expectations by indicating that you will address the new task after you have finished your current priority.