非一日之功

1. • lit. cannot be done in one day (idiom)
2. • fig. will take much time and effort to accomplish

Character by character

• 非(fēi)not be
• 一(yī)one
• 日(rì)sun
• 之(zhī)(possessive particle, literary equivalent of 的 de)
• 功(gōng)meritorious deed or service