Somebody tells me to not come on their property. When does the warning expire? The statute of limitations is about a year, is that enough?
The crime of trespass carries with it the "warning" requirement (alternatively, no warning is needed if you enter "with intent to vex or annoy the owner or occupant thereof, or to commit any unlawful act"). There is no expiration for the oral warning, though the warning method only applies to a "guest", defined as "any person entertained or to whom hospitality is extended, including, but not limited to, any person who stays overnight", (and excluding tenants). It is reported that Clark County prosecutors tend not to prosecute casino trespass cases where the warning is more than a year old, but in principle a permanent ban is possible (hence, call your attorney to negotiate a return, if that is the applicable context).
A civil lawsuit over trespass is also possible, and in that case there is no prosecutor exercising discretion to prosecute or not. Instead, the plaintiff can pursue the case anytime, as long as it is within the statute of limits: an oral or written warning does not "expire".