It depends on data quantity. Report generation can last from fractions of a second to several minutes (when generating detailed report on a long period). BI tools are based on the fact that the source data, downloaded from the source system, are prepared especially for the reports. Therefore “best practices” minimize report generating time. On the other hand, if no of these practices can be used (what happen extremely rare), it is possible to generate report in advance using the tools for scheduling. The final user can receive the most recent report when needed.