1. Search around; there are plenty of scripts that have this already. [Default or Custom CMS]
2. You can do this by eventing, and it'd most likely be easier.
3. Search for ccoa's UMS.
4. Do you mean look like night or an actual time script?
To make it look like night, you'd use events [Tints and stuff]
To make an actual time script, search around here... there's the ATES & ... forget what the other one is called XD