*edit* I just noticed a few posts above mine that others are having the same problem. I posted on the GC page on curse.com, so hopefully the two mods can start to play nice with each other.
That's a Group Calendar issue. If you mean that you can't get the icon itself to show (even if it is a clock), then right click your minimap > show/hide menu > time indicator.
It's probably some conflict somewhere I'm sure. Checking and unchecking the show/hide time indicator doesn't resolve anything with GC enabled.
Lol I know, I know... too many edits. But anyway, I did a little troubleshooting, to figure out if smm is to blame or if it's gc. I logged in to WoW with smm enabled, but not gc, and the time indicator will still not show no matter if it's checked to show or hide. So that tells me smm has an issue somewhere.