I wonder if Time Zone|Sync only syncs the time zone. On my page it shows that router time and browser time don’t match because my router is set to UTC while my browser is US-East. The UTC time itself is correct, and the warning goes away if I manually change the time zone or sync, either. (Beta 4 here).
But you are days off. I wonder if your NTP is working? If you go into Luci, does it show that the NTP client is enabled, and the servers are the openwrt.pool.ntp.org servers?