One day weight gain?

There is a limit to how much you can eat in a day, there is a limit to how much your digestive system could absorb in a day and there is a limit to how much fat your body could store in a day.
Even with a great deal of effort (and money) you would be hard pressed to put on more than a few pounds in a day. To attempt this could be very harmful, for longer lasting, more healthy results attempt to make new muscle tissue, it is more dense (heavier if you prefer) than fat and will last longer.