How long does it take for an online merchant to send a lawyer's letter to sue?

Legal analysis: it's hard to say, some just send letters to play a deterrent role, and some are really ready to sue. Bring a lawsuit within one month at the earliest, and not more than two years at the latest.

Legal basis: Article 5 of the Electronic Commerce Law of the People's Republic of China should follow the principles of voluntariness, equality, fairness, honesty and credibility, abide by laws and business ethics, participate in market competition fairly, perform obligations such as consumer rights protection, environmental protection, intellectual property protection, network security and personal information protection, assume responsibility for product and service quality, and accept supervision by the government and society.