How long a deleted organization name is reserved?

Hi , I hold two organization named “X1” & “X”, In order to merge them I migrated everything from org - “X” to “X1” and deleted org “X”. Many colleagues inside organization feel that “X1” should be renamed as “X” over poll. When I tried renaming organization it errored saying “Organization name ‘X’ is unavailable”

so please let me know How long a deleted organization name is reserved ?