Here in the "lower" midwest, there are two basic "camps". One group of employers gives vacation time as it is earned on an annual basis. First year is usually some "prorated" formula, but after completing one full year, you are placed on the schedule of vacation. 1 week the first year, 2 weeks after "x" years and so on. This vacation can be taken immediately on January 1. Therefore vacation is earned and usually unused vacation is paid upon termination.
The second group of employers will allow their employees to earn vacation time by the month. So, once you have completed the probationary period, you earn "x" hours of vacation for each month of employment and you cannot take it prior to it being earned. Again, this vacation is earned and unused vacation is paid upon termination.
It is less common to give vacation in advance of earning it. Of course, this excludes vacation incentives given to more highly paid employees or highly technical employees.
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"No problem can withstand the assault of sustained thinking." ~ Voltaire
"Sustained thinking gives me a headache." ~Me