Fix time unit in log message for slow acknowledgements

[PatrickGotthard]

📢 Type of change

• Bugfix
• New feature
• Enhancement
• Refactoring

📜 Description

Slow acknowledgements are currently logged in seconds although the value is measured in milliseconds.

💡 Motivation and Context

Bugs should be fixed 👍

💚 How did you test it?

There's nothing to test

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated reference documentation to reflect the change
• All tests passing
• No breaking changes

🔮 Next steps

Merge it 👍

[tomazfernandes]

Thanks for the PR @PatrickGotthard!