Perhaps for people who don't live in the same time zone as what is
used for the server clock, they could know whether it is day or
night on the site. Just like a little sun or moon icon next to
Castform is what I was thinking. This wouldn't be a big thing,
mostly used for time-specific evolutions (i.e, Umbreon/Espeon,
Weavile, Honchkrow, etc.)
You can use the server time at the bottom of every page to see
wether it's day or night.
On top of that, Umbreon & Espeon don't evolve based on time. Check
out the Evolution
Guide.
Hm, maybe the day/nighttime system could affect what type of
Pokemon appear at the honey tree and maybe even how often certain
eggs appear at the lab. Just throwing ideas out there. I sort of
support this, thought like Riako stated, I'm not sure if a sun/moon
would really be needed that much.