--Try this

SELECT

x.patID ,

x.Mdt

FROM

( SELECT

patID ,

MIN(tci.enc_date) AS Mdt ,

CONVERT(DATE, tci.enc_date) AS date

FROM

#tmp_CustInfo AS tci

GROUP BY

patID ,

CONVERT(DATE, tci.enc_date)

) x

WHERE

CONVERT(INT, LEFT(REPLACE(x.date, '-', ''), 6)) % 2 = 1

ORDER BY

x.patID;

--Note: you do not have to use convert inside subquery