You can store and serve diluted syrup for up to 5 days in a sealed container in a refrigerator that holds a constant <4C temperature. This is dependent on proper sanitisation of mixing and storage bottles and caps, and proper cleaning procedures of hands and preparation and storage areas when mixing syrups.
Opened bottles of non-diluted syrup should be used within one month of opening, and stored in a refrigerator that holds a constant <4C temperature.
Unopened bottles of syrup should be stored in cool, dry area away from direct sunlight.
You can find advice on cleaning your machine here.