At the stage you are at I would be considering 2 things.
First, you're almost ready to start training the plant to produce more bud sites. I'd say another node or two and you're ready to top the main stem.
Second, if you want to avoid overwatering try bottom watering. Take a bucket larger than the one you have the plant in and fill it with 6.0 water, lower the pot into the water and let it float around and wick up the water once it gets close to the soil line pull it out and let it drain. This will wet the entire grow media rather than top watering which will create water columns the water creates looking for the path of least resistance to the bottom and out the pot leaving dry spots.
E9noxis's advice is sound. You can confirm how dry they are by picking up the pot and seeing how heavy it is. Obviously when they have just been watered they'll be heavy but after a few days they'll be much lighter through plant uptake and evaporation into the air. Watch the plant and you'll see when it's about to wilt. Pick up the pot and note how light it is so you know when your plant is ready for more water. These plants don't like wet soil. They grow bigger and hardier if you let the soil get semi dry. Letting the soil get dry will also spur the root system to get bigger as it looks for water. Of course when I say "dry" I don't mean bone dry. Lightly damp is where you want to start thinking about watering. Infrequent deep waterings are better than light watering daily so don't water with drips and drabs!
My guess is you need to water them every 3 days from where I'm sitting but your environment and plant uptake plays a big part in how fast your soil will dry out.
If you got the money I would also invest in a soil meter to measure soil PH. As important as it is to PH your feed water ultimately the soil PH will dictate nutrient lockout. I did a grow where I was religiously feeding at 6.0 but the plants looked sickly and weak. Bought a soil PH tester and found out the soil PH was at 4.4. Raised my nutrient PH to 8.0. Soil PH rose to 5.7. Second feeding I set feed water PH at 7.0. Soil PH leveled out at 6.0! Perfect! Continued to monitor soil PH while feed water PH was at normal 6.0. Plants woke up and went on to produce some beautiful Colas!!!!
This will work great for testing soil PH....
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