"My friend keeps insisting that the 6pm deadline is illegal and the case could be thrown out if it goes to court, even if the tenant doesn't pay....any idea?"
We already gave you the best ideas we have. Get to the post office and make the certified mailing of the 3 day pay or quit notice. Start counting the days from the mailing. Allow one day for the mailing and 3 days following that. Make sure you ask for a return receipt of the certified mail. Forget about the previous notice.