3P means 3 hours parking. The 6am - 1pm is the time that is in effect. Outside those times, it's the default time. I don't know what that is in NSW, but around here it is 2 hours. Now whether you a total of 3 hours (i.e. your 2 hours resets at 1pm), of 2 hours total is immaterial. You're talking about parking there for 6 hours, which clearly doesn't fit under either.
So, assuming the 'default' parking time is less than 5 hours (1pm - 6pm), then you've committed an infringement.