The tendency of people to underestimate the time required to complete a task is called the:

The tendency of people to underestimate the time required to complete a task is called the Planning Fallacy.

Explanation:

Understanding Planning Fallacy

Planning fallacy is a particular optimistic kind of biasness, firstly suggested in 1979 by two psychologists namely Daniel Kahneman and Amos Tversky, where we tend to underestimate the time needed to finish a task, however, we have a clear cut idea that last time same kind of task took 2 hours, this time we estimate it to be completed in 1 hour and 30 minutes, therefore it is also the case of overconfidence that we can complete the given task in that much (lesser than actual) time.