Loneliness is also the time when繁华hasn't bloomed yet. (Note: "繁华" usually means prosperity or flourishing, but in this poetic context, it can be interpreted as "繁花", which means "numerous flowers". So a more fitting translation might be: Loneliness is also when the flowers have yet to bloom.) A refined version could be: "Loneliness is also when the flowers have yet to bloom."