5 isn’t too early to count…in fact my own home Parish has the Saturday Vigil at 5pm.
But what matters is which Mass it is…if it is the Saturday Vigil (meaning, it has all the readings for the Sunday Mass even though it happens on Saturday evening) then it fulfills the obligation. If it’s a Saturday Mass (meaning, it has the readings for Saturday’s daily Mass) then I am pretty sure it doesn’t.
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