You can be in Clark County for sixty days without registering your handguns. Residents have 72 hours to register handguns. You can open carry in Las Vegas without a permit, just like in the rest of Nevada.
The preemption statute specifically allows for Clark County to maintain handgun registration. While some are lobbying to get this removed it is the law.
Also, while the law says that regulation is reserved for the state legislature (other than discharge and the allowance of Clark to register), the current Nevada attorney general website says that the law doesn't do anything. North Las Vegas has an ordinance against firearms in vehicles.
If you ask your question in the Nevada section you may get more responses.