They absolutely can be: see https://www.archives.gov/federal-register/electoral-college/..., specifically the section of the US code that speaks to "Failure to make choice on prescribed day" and "Determination of controversy as to appointment of electors". Basically - if for any reason a state can't pick electors on election day, it can do so afterwards by whatever (constitutional) method it desires; and if there's a disputed election and a state has a (pre-election) law enacted for deciding controversies that law just has to come to a decision within 6 days before the electors meet.