The idea was to eat enough protein ( 1.5 x body weight in Kg), keep
working out, and have calorie in < calorie out.
With the above understanding, you're on the right track.
Since you're allowed to eat and exercise during the night, it seems that you've basically inverted the day-night cycle as far as nutrition is concerned because quite a few people sleep for 8-10 (your 16 hour fast is still longer) hours a night without eating or drinking in between.
If there's absolutely nothing you're allowed to eat/drink during the day then the only thing that you can really do is to ensure that your body gets sufficient nutrition and exercise during the night and that you take long lasting / slow digesting Casein like protein in the morning.
If I were you, I would exercise in the evening (after taking a decent protein, BCAAs and other nutrient rich pre-workout shake or a light meal), then take a solid high quality protein meal post-workout and potentially a few protein shakes/bars if I wake up during the night (unless you can just have another solid meal 4-5 hours into the night) followed by another high quality long lasting protein (Casein, for example), BCAAs and nutrient rich solid meal in the morning to last me the day. Casein or equivalent would last for 7-10 hours depending on what else you've eaten giving you a steady trickle of protein for most of the day.
All that slow digesting protein might make you more thirsty than usual (my personal experience, everyone is different), but I guess there's just no way around it other than drinking a lot of water during the night and morning if you can't drink water during the day.