4PM is the general earliest time, but there are some Churches which have received permission to offer Sunday mass even earlier. For example, the Cathedral in Las Vegas offers a 2:30 PM Sunday Mass on Saturday for all the tourists.
Just an interesting tidbit I picked up about the vigil Mass is that originally they were designed for people who could not make Mass on Sunday for legitimate reasons, like essential work responsibilities (police, firefighter, etc.). I’ve always felt a bit weird about going to Mass on Saturdays. Don’t get me wrong - I go to vigil Masses, too, but after learning this, I will make a bigger effort to go to Mass on actual Sundays. Another thing I learned is that no vigil Latin Masses are offered on Saturdays.
Just to clarify the terminology here, what you are referring to is an"anticipated Mass," that is, a Sunday Mass celebrated on Saturday evening. A “vigil Mass” celebrated on the day before a major feast such as the Nativity of St. John the Baptist is something entire different. But the term is commonly misused including on 9 out of 10 web sites I just “googled.”
And to really spell it out, a Saturday evening Mass does not have to use the Sunday readings to fulfil the obligation, a consideration which was implied in the OP’s original question… Even a Nuptial Mass would fulfil it., provided that the time was late enough.Just to clarify the terminology here, what you are referring to is an"anticipated Mass," that is, a Sunday Mass celebrated on Saturday evening. A “vigil Mass” celebrated on the day before a major feast such as the Nativity of St. John the Baptist is something entire different. But the term is commonly misused including on 9 out of 10 web sites I just “googled.”
That being said, any Mass (anticipated, vigil, nuptual and so forth) celebrated on Saturday evening fulfills one’s Sunday obligation.