Is it possible to make 2 VOA in Zhuhai at a few days of interval

And how is the time calculated? If I enter on October 8th, I need to leave on October 11th, correct?

1. If you don't have special interest to visit Hong Kong, you can take CKS - Chu Kong Passenger Transport ferry (catamaran in reality) directly from HKIA Skypier to Zhuhai Jiuzhou port. In this way, you will skip Hong Kong immigration and will apply for Zhuhai VOA on arrival at Jiuzhou port. The ferries from HKIA Skypier depart at: 10:20, 14:15, 17:20 and 21:00. If you intend to visit Hong Kong, then your best option is to take a bus via HZMB bridge where you will apply for a VOA at Zhuhai port of entry.

2. You will easily reach Macau from Zhuhai. You will just walk from Zhuhai to Macau via Gongbei border crossing. After your visit to Macau, you will walk again across Gongbei crossing where you will apply for your second Zhuhai VOA and, yes, this is legal and allowed.

3. You can use direct ferry from Zhuhai Jiuzhou to HKIA Skypier or you can go again to Hong Kong and from there to HKIA.

The time is calculated in the way as you have mentioned. The day of arrival is not counted against 3 days that you are allowed to stay in Zhuhai. In other words, it is your day of arrival + 3 days. Anyway, you have to take care to exit before the midnight of the third day!