This probably could be included in the next version, but currently next version is not coming soon.
If you want to modify the source, and recompile, this could be the change:
In the file smsd.c:
if (DEVICE.message_limit > 0 &&
message_count == DEVICE.message_limit)
char timestamp; //new
writelogfile0(LOG_WARNING, 0, tb_sprintf("Message limit %i is reached.", DEVICE.message_limit));
make_datetime_string(timestamp, sizeof(timestamp), 0, 0, 0); //new
//sprintf(msg, "Smsd3: %s: Message limit %i is reached.", process_title, DEVICE.message_limit);
sprintf(msg, "Smsd3: %s: Message limit %i is reached at %s.", process_title, DEVICE.message_limit, timestamp);
send_admin_message(&quick, &errorcounter, msg);
'c' Syntax Highlight powered by GeSHi
Note: I have not tested this change, I'm unable to compile right now...