With proper firewall rules, the GUI is accessible on any of its interfaces, including the WAN IP address 192.168.0.25. To make this work, go to Firewall -> Rules, click on WAN tab and add a rule to allow https traffic to the WAN IP address:
protocol TCP, source IP any, source port any, destination IP 'WAN address', destination port 443 (https).
Move this rule to the top (at least before any rule that blocks traffic) and apply
Now you can access the GUI via
https://192.168.0.25