Would particularly like the opinion of a lawyer or HR person re telling "white lies" to employers, is it legal?

A lie is a lie. But if it has nothing to do with business, it's none of the employer's business. In your example 1, it's absolutely none of their business. In 2, yes it's business related, but you're right, is so common that most employers wouldn't even ask. In 3, they should say that they need to leave early to deal with a personal issue, and if more questions are asked, say it's personal. And the employee has no requirement to tell his boss about a trial separation.