The IP address clearly isn't causing the issue, because access to the web interface is unaffected. I do have a section of reserved DHCP addresses in my router, but I also have another device, that is a complete pain, if other devices are using DHCP. That is why I allocate devices to fixed regions of addresses, so I know things have no conflicts.
This isn't a router issue, so I don't want to change how my network is handled, because of another device that doesn't work properly. I need to resolve the issue at the source, which is the NAS. Call me stubborn, but 30 years of writing software teaches you to fix the bug where it exists, not to fix everything else to work round it. Just a philosophy I stick to I'm afraid.
Edit: Just to show I am not being totally obstructive... I did change it to DHCP, and it connected via windows explorer... I then changed it back to static, and it connected again. So it looks like something in the upgrade, caused a network glitch, that switching modes has fixed. Sadly, this isn't the first device I have seen with this kind of problem... It's almost like some kind of network profile gets created, and doesn't get flushed after an upgrade... then again, had I been able to save the config settings, I could have done a reset to factory default.
I won't know if the scheduling has been fixed until tonight, as this will be the first day that it has turned on and off by the schedule. I will update later/tomorrow with the results of that.