When it comes to bathing, the behaviour exhibited depends on the budgie itself, there is not a norm regarding a set time that takes for a budgie to become interested in the birdie bathtub and really use it. Nor is there a norm regarding how often they take these baths.
Some budgies never use a birdie bathtub, while others can take months or even years to first use one.
It all depends on the budgie's preferences and level of curiosity.
Some budgies would rather take baths on wet leafy greens while others love to wash their faces, little heads and chest on the water container.
There are also budgies that like being misted with a spray bottle and others that make good use of the birdie bathtubs.
It's great that your budgie girl has decided to try out her bathtub and is enjoying her baths!