I'm not sure if you are talking about a three-day notice to pay rent or quit, since you've marked your question as "employment," but if this is a landlord/tenant or eviction-type question, then, no, you are not correct.
If the notice was delivered on Saturday, you start counting the three days the next day (Sunday), regardless of whether it was a weekend or holiday. In this case, the rent must be paid or you must 'quit' on Tuesday by midnight.
Assuming you intended to post this in the employment practice area, I can only further assume you are talking about a three days notice from the employer that something was going to happen, or a three day notice from the employee to the employer of some decision.
In the employment context, it would be reckless to assume that a notice giving you three days to act will be counted in business days. Assume actual calendar days. Do not count the first day when the deadline was communicated. Start counting with "1" being the next day.
If you need more, you will have to be far more specific to assist us in assisting you.
Good luck to you.
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