I'm a manager who has to speak directly to paying customers about how long they have to wait to get what they paid for and even I will never give a deadline or date. Most customers are actually pretty reasonable and know you can't predict everything. Most are thoroughly aware of how terrible they are at giving clear direction. It's important as a leader to exactly why things take time or why timing is unclear. Risks, uncertainty, quality takes time. There's also plenty of things you can do as a manager to de-risk a delivery and avoid being bottlenecked by risky tasks. It's also much easier (not easy, but easier) to estimate larger buckets of tasks than individual ones knowing that some will be harder than expected and some will be faster.
