mysql -e 'update jalalarm set utime='2005-12-6" 18\:00\:00"' ' -u root -pmysql tgc

Unknown command '\:'
how to overcome

There's complex quoting in your statement: escaped ': ' within double quotes, which are within single quotes within yet another set of single quotes. Probably the problem is in the quoting / escaping.

Do you really need the '\' in front of the ':' ? It's already within quotes.

What exactly do you want to do with: set utime='2005-12-6" 18\:00\:00"'

Try first to put your SQL command in a file instead of on the command line, and execute it with:
mysql -u root -pmysql tgc <file-with-sql.txt

Try at first to use as little quoting/escaping as possible, and add them as needed.

update jalbk set utime = '2004-09-27 18:00:00' where sdate < '2004-03-15 18:00:00';
i m writting this code in a file and then executing
not working