Expectation management is a factor that can affect a customer's experience. A way to manage expectations is to give estimated timelines. Offer estimates and make that hard to miss - If there is a chance the estimated timeline would be surpassed, Communicate that beforehand.
In summary, avoid giving definite timelines. For example, We'll get this done in 48hrs.
Also, it's a good idea to give extra time when setting timelines. If it would usually take 48hrs, you could add another 24hrs. And then say, we'll get this done within 72hrs. Or, it would take 2 - 3 business days.
Giving definite timelines and not seeing them through causes people to lose faith in you and your product. Reliability is another important factor in customer and user experience.
If your customers do not trust that your service would be available 98% of the time, they might move to a more reliable service even if they have to deal with some trade-offs. At least, it works.