create a text file under /etc/squid/ and enter the time range to configure time limit..

# vim /etc/squid/time.txt
11:00-11:15
14:00-14:15

now configure acl rule... on /etc/squid/squid.conf file.

acl test src 192.168.7.210 192.168.7.211

acl downtime  time  "/etc/squid/time.txt"

http_access deny test downtime  

http_access  allow test

and finally restart the squid service.