Mysql variables

Is there a restriction that's causing the following problem? Local variables seem to cause no results. I could get around this with inline values and parameters, but just good to know.

These work in mysql workbench:
set @interval_months = 5;
set @tz_adjust = TIMESTAMPDIFF(HOUR, NOW(), UTC_TIMESTAMP);

results in:

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SQL: /*
Data from x months ago until yesterday
*/
set @interval_months = 5;
set @tz_adjust = TIMESTAMPDIFF(HOUR, NOW(), UTC_TIMESTAMP);
select ticketid,FROM_UNIXTIME(dateline) AS 'Created Date',email,ownerstaffname,firstresponsetime/3600 AS 'Response Time' from swtickets LIMIT 100;

SQL: /*
Data from x months ago until yesterday
*/
set @interval_months = 5;
set @tz_adjust = TIMESTAMPDIFF(HOUR, NOW(), UTC_TIMESTAMP);
select ticketid,FROM_UNIXTIME(dateline) AS 'Created Date',email,ownerstaffname,firstresponsetime/3600 AS 'Response Time' from swtickets LIMIT 100;

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