Here's a lua cheat that works with the change just pushed for zelda that sets the clock. Put it in "cheat/gnw_zelda.json" and run mame with "-plugin cheat" and look in Plugin Options/Cheats.
It seems to be giving me an error: attempt to index a nil value(global 'os')
Oh wow that's awesome it works! I do have some feedback though. The cheat set it to 12 pm instead of am, and the alarm didn't work because of this I'm assuming.
Is there a way to make the cheat toggle activated to make sure the time is synced at all times? The main issue I have is that since it's emulation the timing might not be spot on and drop out of sync. That's the biggest issue I have with the clock in these G&W emulations.
I might try to mess with the script myself but I never messed with lua before.