This essentially means doing all the shaving/trimming/waxing before applying any tanning products. You don't want to get streaks or have a blotchy tan.
Technically you could use your hands to apply the product onto your skin but I'm telling you from experience your hands are going to be blotchy use mitts instead. Plus, your tan will look more smooth.
This is a common mistake especially when it's your first time. Make sure to apply an even and somewhat thick layer so you can have a more noticeable tan.
Color development takes about 4-6 hours. So longer you keep the product on your skin, the darker your skin will get. Obviously not any darker than the product or the shade you chose so no worries on that part.
This is true for any tan even the natural tan. By moisturizing your skin, your tan is going to last longer and will look more smooth. Our body naturally exfoliates so with the moisturizer you're just extending that period just a little longer.