This stand is open daily from 7h30 am up to 9 pm. The staff doesn´t speak English but their daughter (who is often there) does and they are nice.
The place is not so easy to spot but if you look for Wan Chai market (in Zenith Tower), it is just opposite one of its entrances (check the photo here).
It is a stand selling fruits and they make also inexpensive (10-12, some at 15 HKD) fresh fruit juices to take away (one size - medium size cup) without any additives (no sugar...), made in a centrifugal juicer. There is on offer: watermelon, carrot, mango-pear, pear, grape, apple, dragon fruit, guava, star fruit, wax apple, papaya-pear, lemon-orange, orange, grapefruit, kiwi-apple, blueberry-apple, bitter melon, pineapple-orange, vegetable and celery juice.
Cons: Not always English-speaking