Sorry for the galaxy issue, they're pretty broken right now. Improving them (and bringing them up to par with Legacy) has been on our list for a long time now. The good news is that we have a developer who's very excited to dive into this project once we are done with our next VR update. Hopefully soon they'll be mapped properly and actually have distinct shapes, rather than the generic blobs most of them have now.
As for setting a specific date & time, you can't do that while running a sim, but you can start a sim at a specific date. Before opening a sim, hover over its tile (in Home > Open), then click the pencil icon to Open Advanced Settings. There you can specify a date and time.
Hope that helps!