Protein shakes and smoothies are best consumed in the morning and in the evening, before or after a workout respectively. One way around this is to set an alarm on your smartphone for two times per day, and prepare the shakes accordingly.
The reason we recommend four hours before bedtime is because insulin will make you fatigued (insulin makes cells accumulate sugar, which it then uses as energy). And fasting overnight tells your body that it may need to push that fat into its stores, when if you take in sugar during the night it could start burning all of those last few cells of energy left behind from when it thought you were starving.