I've not understood this question when you posted it in the past. Are you saying you want to have SARG generate a daily report? Probably the simplest solution is to rotate the access logs daily using logrotate.
Create a file called "squid" in /etc/logrotate.d/ with the following content:
This generates a new squid log every day and preserves the prior fifteen days of logs in /var/log/squid.
/usr/sbin/squid -k rotate 2>/dev/null