Excuse me, if I send a postcard from Japan to China and throw it in the mailbox, how long will it take to receive it?

Leaflets? It's best to send postcards in envelopes and put things in them at the same time, so that they look full and are not easy to lose. However, if you put things in, you'd better post enough postage. If you send it from abroad to China, you'd better tell the staff what the postage is and how to send it, otherwise your filling process will be different and you may lose it! It usually takes 1 month to 2 months to send it from abroad to China. If the character is poor, it is possible to collect it after two years.