If people don't know how much time something is gong to take they can often give up, or not do it at all.
Always provide progress indicators to tell people how long something will take.
Make processes seem shorter by breaking them up in sections for the audience. Mental processing is what causes things to seem like they take a long time.
You want to let people adjust their expectations accordingly to the process so it's best to keep the task time short, or to consistently inform them of information.