How to group many role playing time dimensions in one time dimension?

Just set the Visible property of all time dimensions to False, add a new time dimension, and replace all measures by calculated measures. Each calculated measure should use the LINKMEMBER function in order to use the visible time dimension instead of the other hidden time dimensions.

Below an example of a calculated measure: 

([Measures].[MyMeasure], LINKMEMBER([Date].[Year].CURRENTMEMBER, [Date Hidden].[Year]), LINKMEMBER([Date].[Date].CURRENTMEMBER, [Date Hidden].[Date]), LINKMEMBER([Date].[Week].CURRENTMEMBER, [Date Hidden].[Week]), LINKMEMBER([Date].[Month].CURRENTMEMBER, [Date Hidden].[Month]), LINKMEMBER([Date].[Calendar].CURRENTMEMBER, [Date Hidden].[Calendar]))