How does the length of time that a soda bottle is open affect its fizziness?

Because all soda is carbonated the longer it is open the less "frizzy" it will be.

As the carbonated soda and flavored syrup are exposed to air they release carbon dioxide gas which release and do not recombine with the liquid.

Depending on the level of carbonation it can take anywhere from a few minutes to a few hours for all of the the co2 to escape.

Don't try this on beer or champagne unless you are conducting a well funded scientific experiment.

Waste soda not happiness.