Looking at how much time it takes to fill up a Nightclub in GTA it roughly breaks down like this:
South American Imports takes roughly 20 hours, while Cargo is about 59 hours. Pharmaceuticals takes approximately 20 hours, Sporting Goods takes a little over 66 hours and Cash takes around 20 hours.
What is the Best Way to Maximize the Income of the Club?
If you have the option of playing a little each day and then leaving the console running AFK overnight you can make the most of it by selling every 15-20 hours as opposed to waiting for it to fill up completely. For example, with the bunker, when you come on the next day you can resupply it immediately for about 75k and sell the stock for around 200k. Then if you are going to be playing for a couple of hours you can sell the stock it’s built and resupply it before going AFK again.
Apply this same style of method to the others like the nightclub (minus things like Tony’s fee) and as long as you’re keeping track of buying costs, wages and utility bills, and playing some missions in between, you can be earning over 1 mil just for playing for a few hours each day.
Do I Have to Keep Interacting with the Nightclub?
Not particularly. Your Nightclub is separate from your Warehouse so you don’t necessarily need to interact with it. Just keep in mind that the maximum amount it can hold is 70k. Above 70k it is used by Tony and has a fee every 48 hours.
Is it Safe to Leave my Console Running All Night?
Most users have no issues leaving their consoles running for prolonged periods of time. The designers have created them to run for extended periods of time.