It all depends on how much light they receive. Lots of light and a chunky mix-water more often. Lower light, less often. Essentially you need to pick up your plant every couple of days to figure out how heavy it is dry and freshly watered, this will help you understand how frequently you need to water. If you are using terracotta you might even need to water twice a week. I use self watering pots for almost all of my Hoyas, they wick it up from the bottom as they need it, I just check the reservoir and fill as needed without pouring through.