Depends on what you start them in. If I start mine in a tray with cells then I wait until they get transplanted into a 4x4 container usually after the 1st true leaves, It has to have roots long enough to reach.
Procedure for Bottom-Watering your Chillies
Place your containers in the plant tray and fill the tray with at least 1 inch of distilled water. Let the water stand for at least 10 minutes and then stick your index finger up to the second knuckle in the soil to ensure that it’s wet. If it’s not, let the water stand for another 10 minutes and then repeat the test. Pour out the water in the tray and then dry it completely to ensure that your pots do not sit in the moisture. As a tip, try picking up the container to get a sense of how it feels when your pepper seedlings are properly watered. Continue to water your peppers when the tray feels lighter, indicating that the soil mix is dry.
Watering Your Hot Peppers in Outdoor Containers
Larger outdoor containers may also be watered from the bottom. Obtain a large container, such as an inflatable swimming pool or trough, that is large enough to hold the pepper pots. Position the pots in the container and fill it with water so that the it reaches halfway up the pots. Leave the water for about 30 minutes to an hour to allow the pepper roots to soak up all the moisture. Again, lift the pot to get a feel for how heavy it should be when the hot pepper plant is sufficiently hydrated. Use this bottom-watering technique when your pots are light, or stick a moisture meter in your pepper soil to determine if its ready for another watering.