A Progress indicator signals that an application is busy performing an operation.
When operations take five seconds or longer to complete, add a progress feedback element to your design.
Rules of Thumb
Use Indeterminate Progress mode to continually display unknown progress for an operation.
Use Determinate Progress mode when an operation has a well-defined duration or a predictable end.
Don’t provide inaccurate time or percentage estimates if the precise completion time for the operation is unknown.