from mIRC help files:
Changing a standard CTCP reply
ctcp 1:ping:?:/notice $nick Ouch! | /halt
This will react to the standard ping CTCP and will reply with "Ouch!". The /halt at the end of the line prevents the standard ping reply from being sent. If you don't use the /halt, the standard reply to PING will be sent.
ctcp 1:time:?:/notice $nick The time here is around $time | /halt
This will react to the standard time CTCP and will reply with the above message. Again, the /halt prevents the standard time reply from being sent.
so try
ctcp *:time:?:{
notice $nick $asctime(mm/dd/yy hh:mm TT)
halt
}