No it decreases
As long as they have flue to heat the balloon.
invisible string
Hot air balloons rely on the temperature difference between the air inside and outside the balloon to generate lift. As you ascend, the temperature of the air outside the balloon decreases, reducing the lift. At higher altitudes, the balloon would need a larger temperature difference to stay afloat, which is difficult to achieve with a burner.
The duration an air-filled balloon stays inflated can vary based on factors such as the quality of the balloon, temperature, and air pressure. Under normal conditions, an air-filled balloon can stay inflated for several days to a week before starting to deflate.
the buoyancy
The question is not well-formed. Similar questions may include: How many minutes does a helium balloon stay aloft? How long does a hot air balloon stay aloft? How long does a particular rocket motor burn?
Yes
There is no weight in an empty balloon. Empty balloons will not stay on the ground long enough to have any real weight.
I presume you mean without an airborne heater. The answer is, there is no fixed time! It could range from a few minutes to the best part of a day. It all depends on the rate the balloon loses heat, which in turn depends on the size of the balloon, the weight of the balloon, the insulation and porosity properties of the balloon fabric, and the amount of solar heating, if any, that it receives.
balloon stay up because of the air inside it. to make the balloon stay up the air should be light. inside the balloons you can find the air we called helium. helium is a light air that makes the balloon stay up. that's why if you blow the balloon it wont float because the air that comes from your mouth is not helium but carbon dioxide and carbon dioxide is heavier compared to helium so it wont float.
A weather balloon can stay in the air for several hours to a few days before descending back to the ground. The exact duration depends on factors such as the size of the balloon, the altitude it reaches, and weather conditions.