2 Tag length can be 35, change the get date as UTC
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You can add the Period in months as integer and handle with DATEADD in the WHERE clause as (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETDATEGETUTCDATE()) AND GETDATEGETUTCDATE()).

Query in SEDE

DECLARE @Tag VARCHAR(2535) = '##Tag##'
DECLARE @Period INT = '##Period##'

SELECT TOP 50 Q.Id AS [Post Link], 
    Q.Tags, Q.AnswerCount, Q.ViewCount
FROM Posts AS Q
INNER JOIN PostTags AS P ON P.PostId = Q.Id
INNER JOIN Tags AS T ON T.Id = P.TagId
WHERE T.TagName = @Tag AND
      (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETDATEGETUTCDATE()) AND GETDATEGETUTCDATE())
ORDER BY Q.ViewCount DESC

You can add the Period in months as integer and handle with DATEADD in the WHERE clause as (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETDATE()) AND GETDATE()).

Query in SEDE

DECLARE @Tag VARCHAR(25) = '##Tag##'
DECLARE @Period INT = '##Period##'

SELECT TOP 50 Q.Id AS [Post Link], 
    Q.Tags, Q.AnswerCount, Q.ViewCount
FROM Posts AS Q
INNER JOIN PostTags AS P ON P.PostId = Q.Id
INNER JOIN Tags AS T ON T.Id = P.TagId
WHERE T.TagName = @Tag AND
      (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETDATE()) AND GETDATE())
ORDER BY Q.ViewCount DESC

You can add the Period in months as integer and handle with DATEADD in the WHERE clause as (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETUTCDATE()) AND GETUTCDATE()).

Query in SEDE

DECLARE @Tag VARCHAR(35) = '##Tag##'
DECLARE @Period INT = '##Period##'

SELECT TOP 50 Q.Id AS [Post Link], 
    Q.Tags, Q.AnswerCount, Q.ViewCount
FROM Posts AS Q
INNER JOIN PostTags AS P ON P.PostId = Q.Id
INNER JOIN Tags AS T ON T.Id = P.TagId
WHERE T.TagName = @Tag AND
      (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETUTCDATE()) AND GETUTCDATE())
ORDER BY Q.ViewCount DESC
1
source | link

You can add the Period in months as integer and handle with DATEADD in the WHERE clause as (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETDATE()) AND GETDATE()).

Query in SEDE

DECLARE @Tag VARCHAR(25) = '##Tag##'
DECLARE @Period INT = '##Period##'

SELECT TOP 50 Q.Id AS [Post Link], 
    Q.Tags, Q.AnswerCount, Q.ViewCount
FROM Posts AS Q
INNER JOIN PostTags AS P ON P.PostId = Q.Id
INNER JOIN Tags AS T ON T.Id = P.TagId
WHERE T.TagName = @Tag AND
      (Q.CreationDate BETWEEN DATEADD(MONTH, -@Period, GETDATE()) AND GETDATE())
ORDER BY Q.ViewCount DESC