Some ISP's block NTP requests in their router firewalls. Some ISP's block NTP in their network. It's stupid, but it happens.
You can try configuring 0.br.pool.ntp.org, 1.br.pool.ntp.org, 2.br.pool.ntp.org and see if those work? - also set the LAN IP of the router and see if that works as an alternative - you'll be at the whims of the router clock but at least you'll probably get something within the same day.