Look at the lines before that. What I can see in this log is that ntp is restarting the upnp and disk monitoring services. We need to see what caused the ntp service to restart. Walk our way back up the chain until the source of all those service restarts.
But the lines before that says the date is from Dec. 31st and I just got this router less then a week ago. The information on those lines does not seem to correlate with today's disconnection date. Here are the lines before the problem occurred.
Dec 31 19:00:14 disk monitor: be idle
Dec 31 19:00:15 Samba Server: daemon is started
Dec 31 19:00:15 dnsmasq[290]: read /etc/hosts - 5 addresses
Dec 31 19:00:16 dnsmasq[290]: read /etc/hosts - 5 addresses
Dec 31 19:00:16 dnsmasq[290]: using nameserver 75.75.76.76#53
Dec 31 19:00:16 dnsmasq[290]: using nameserver 75.75.75.75#53
Dec 31 19:00:16 start_nat_rules: apply the nat_rules(/tmp/nat_rules_eth0_eth0)!
Dec 31 19:00:16 dnsmasq[290]: exiting on receipt of SIGTERM
Dec 31 19:00:17 dnsmasq[374]: started, version 2.68 cachesize 1500
Dec 31 19:00:17 dnsmasq[374]: asynchronous logging enabled, queue limit is 5 messages
Dec 31 19:00:17 dnsmasq-dhcp[374]: DHCP, IP range 192.168.1.2 -- 192.168.1.254, lease time 1d
Dec 31 19:00:17 dnsmasq-dhcp[374]: DHCP, sockets bound exclusively to interface br0
Dec 31 19:00:17 dnsmasq[374]: read /etc/hosts - 5 addresses
Dec 31 19:00:17 dnsmasq[374]: using nameserver 75.75.76.76#53
Dec 31 19:00:17 dnsmasq[374]: using nameserver 75.75.75.75#53
Dec 31 19:00:17 dnsmasq-dhcp[374]: DHCPREQUEST(br0) 192.168.1.129 50:1a:c5:20:14:d8
Dec 31 19:00:17 dnsmasq-dhcp[374]: DHCPACK(br0) 192.168.1.129 50:1a:c5:20:14:d8 XBOXONE
Dec 31 19:00:17 dnsmasq-dhcp[374]: DHCPREQUEST(br0) 192.168.1.129 50:1a:c5:20:14:d8
Dec 31 19:00:17 dnsmasq-dhcp[374]: DHCPACK(br0) 192.168.1.129 50:1a:c5:20:14:d8 XBOXONE
Dec 31 19:00:17 kernel: nf_conntrack_rtsp v0.6.21 loading
Dec 31 19:00:17 kernel: nf_nat_rtsp v0.6.21 loading
Dec 31 19:00:17 rc_service: udhcpc 341:notify_rc stop_upnp
Dec 31 19:00:17 rc_service: udhcpc 341:notify_rc start_upnp
Dec 31 19:00:17 rc_service: udhcpc 341:notify_rc stop_ntpc
Dec 31 19:00:17 rc_service: udhcpc 341:notify_rc start_ntpc
Dec 31 19:00:17 dhcp client: bound 71.226.1.60 via 71.226.1.1 during 283462 seconds.
Dec 31 19:00:17 miniupnpd[411]: HTTP listening on port 39696
Dec 31 19:00:17 miniupnpd[411]: Listening for NAT-PMP traffic on port 5351
Dec 31 19:00:18 WAN Connection: WAN was restored.
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPDISCOVER(br0) 7c:1e:52:57:4f:58
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPOFFER(br0) 192.168.1.231 7c:1e:52:57:4f:58
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPDISCOVER(br0) 7c:1e:52:57:4f:58
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPOFFER(br0) 192.168.1.231 7c:1e:52:57:4f:58
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPREQUEST(br0) 192.168.1.57 e4:8b:7f:a2:ab:b5
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPACK(br0) 192.168.1.57 e4:8b:7f:a2:ab:b5 Dungs-iPad
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPREQUEST(br0) 192.168.1.231 7c:1e:52:57:4f:58
Dec 31 19:00:20 dnsmasq-dhcp[374]: DHCPACK(br0) 192.168.1.231 7c:1e:52:57:4f:58
Dec 31 19:00:40 dnsmasq-dhcp[374]: DHCPREQUEST(br0) 192.168.1.146 c8:33:4b:30:2f:83
Dec 31 19:00:40 dnsmasq-dhcp[374]: DHCPACK(br0) 192.168.1.146 c8:33:4b:30:2f:83 Dungs-iPhone-4S