No shifts when I was working there
You do need to work both shifts but if you're a hard worker with good time keeping and attendance and you have something on every now and again and need a shift change there usually wont be an issue with it. you only need to ask. wherever they can be flexible they will be. I've had childcare issues far more than expected recently and they have been amazing, ive not had to have wages deducted ive just been able to agree to an extra hour where suitable to make the time back
They have no flexibitly with there shifts and will make you make back time if you have a valid doctors appointment.