This option was selected because it does not require an IIS reset (like using Global Time) and it only requires metadata changes once a year since monthly the only change needed is to a security group.
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M1" description="" accessGroup="SLICE_NO_ACCESS_M1" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M2" description="" accessGroup="SLICE_NO_ACCESS_M2" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M3" description="" accessGroup="SLICE_NO_ACCESS_M3" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M4" description="" accessGroup="SLICE_NO_ACCESS_M4" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M5" description="" accessGroup="SLICE_NO_ACCESS_M5" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M6" description="" accessGroup="SLICE_NO_ACCESS_M6" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4,2021M5)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M7" description="" accessGroup="SLICE_NO_ACCESS_M7" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4,2021M5,2021M6,2021Q2,2021H1)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M8" description="" accessGroup="SLICE_NO_ACCESS_M8" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4,2021M5,2021M6,2021Q2,2021H1,2021M7)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M9" description="" accessGroup="SLICE_NO_ACCESS_M9" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4,2021M5,2021M6,2021Q2,2021H1,2021M7,2021M8)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M10" description="" accessGroup="SLICE_NO_ACCESS_M10" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4,2021M5,2021M6,2021Q2,2021H1,2021M7,2021M8,2021M9,2021Q3)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M11" description="" accessGroup="SLICE_NO_ACCESS_M11" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4,2021M5,2021M6,2021Q2,2021H1,2021M7,2021M8,2021M9,2021Q3,2021M10)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
<cubeDataCellAccessItem category="TEST SLICE WITH TIME M12" description="" accessGroup="SLICE_NO_ACCESS_M12" ScenarioMemberFilter="S#Actual" TimeMemberFilter="T#2021.TreeDescendantsInclusive.Remove(2021M1,2021M2,2021M3,2021Q1,2021M4,2021M5,2021M6,2021Q2,2021H1,2021M7,2021M8,2021M9,2021Q3,2021M10,2021M11)" behaviorInGroupInFilter="ApplyAccessAndContinue" accessLevelInGroupInFilter="NoAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="IncreaseAccessAndContinue" accessLevelNotInGroupInFilter="ReadOnly" />
This solution worked best for this customer and use case. No metadata changes monthly, only security group changes. And no IIS reset required for change to take effect. Once a year maintenance to metadata slices and security groups.