Maybe we can find the answer in this Harvard publication?
The Honesty at Work Collection
When is the right time to be honest and open in the workplace? The answer is: always.
In 'The Danger of Silencing Conflict at Work' (Faculty Lecture on CD-ROM), HBS Professor Leslie A. Perlow uses three studies to show that silencing conflict can have devastating negative task and relationship consequences. Her research shows that the best way to complete a task on time and maintain positive working relationships is to communicate openly and honestly.