Capsaicin intensifies during fermentation — the chilli will be noticeably hotter in the finished bottle than when you added it. Start with a smaller slice if you are unsure about the heat level and increase next batch.
Summer (above 24°C): ready in 24-48 hours.
Spring and autumn (20-23°C): 2-3 days.
Winter (below 20°C): 3-4 days.
If it is too spicy, dilute with plain finished kombucha or pour over ice.