VOA 5-day ShenZhen at Luohu port of entry

1. Theoretically, you are eligible for the 5-day VOA. However, recently there is a long line waiting in front of the office, so you may wait for a long time and there is also a risk of rejection.
2.If you get a VOA, you can only stay in Shenzhen.

Singaporean citizens are eligible for Shenzhen 5 days visa without any doubt. You can obtain one at Luohu border crossing, but you are advised to be at the crossing before 09:00 because of high pressure on visa office. Be warned that waiting times can be of several hours.

With Shenzhen VOA you are allowed to stay within Shenzhen city limits only. You are not allowed to travel to any other administrative area within Guangdong Zhuhai included. You would need a separate VOA for Zhuhai, but you cannot do that from Shenzhen, but you have to exit from Shenzhen back to Hong Kong or Macau and then enter to Zhuhai.

My suggestion for you would be to fly from Hong Kong to Guangzhou and exit by ferry to Macau. Like this, you would be eligible for 144 hour visa free transit in entire Guangdong province. The only small drawback in this option is in the fact that you have to book your ferry ticket before your deprature for Guangzhou, you have to print out that ticket and have it with you. Also, you have to exit by exactly that ferry you have bought the ticket for in advance.