You can transfer the batter to a pastry bag fitted with a plain tip or simply use a freezer bag. This will make it easier to fill the madeleine mould.
The raw batter will keep for 3 to 4 days in the refrigerator. But the madeleines are best when baked the same day the batter is made.
In order to bake all of the batter the same day, wash out the madeleine mould and let it cool before repeating step 4.