Vizubi is a excel self-service Business Intelligence plug-in.
Time dimensions are used to filter data against time. For instance if you wanted to see sales for a specific period (this year, this month, last quarter), then you would need to create a time dimension.
Time dimensions are always linked to a time or date in the data (for instance sell date, purchase date, expiry date etcetera). When you import a table or file which has a field which Vizubi recognizes as being in date/time format, Vizubi will automatically create a time dimension linked to that column.
Data in that table or linked to that table can then be filtered against the time dimension.