We all have it, problems that prove difficult to fix and working out a fix through obscure code and bizarre unexpected functionality. Slowly, logically working your way through trying to find patterns, errors, mistakes. This process takes time and the issues are often not easily understood by the client.
How does one answer when asked the question "When will it be done?", especially when the client may not understand the inherent complexities of software development?
Best Answer
You answer the question honestly.
You tell them it's a difficult problem, the solution is not obvious, and you are not sure how long it will take to resolve. Promise to update them on your progress every [time frame], so they know you're working on it, and of course, actually send them the updates.