Timestamp conversion in log

the log format is as follows
log

REQ    UP    15275791948097993    POST    /    {"Content-Length":"61926",xxxxxxxxxx}
REQ    UP    15275791948097993    POST    /    {"Content-Length":"61926",xxxxxxxxxx}

grep xxxx log | awk-F""{print strftime ("% Y-%m-%d% H:%M:%S", $3) $0}"

when the timestamp is 10 digits, the above command can be executed normally and parse the correct time, but here the timestamp is 17 digits, how can the time be parsed normally?

Log
Mar.14,2021

try intercepting the top ten places with ${$3:0:10} syntax

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b33470-2be74.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b33470-2be74.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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