The homepage KV said mobile has no time limit. But when I play, it still tells me my 8 hour trial expires and need purchase. P.S. I use the same account on PC

Did you create your account on Android or through the web site? If you initially logged in on Android, then your account is set as a free-for-mobile account. But if you first logged in on PC then your account is a trial account.

Please submit a support ticket and we can possibly change your account from trial to free-for-mobile with the set of gameplay restrictions that apply to free-mobile accounts.

So after registering in Android we can play on the PC with F2P?

No, F2P accounts require a lite subscription to play on PC. It is only 0.99c a month, and has the same limit as the F2P accounts, but Android made accounts can only play on Android devices. (you can log into the account on a PC, but you only get 5 minutes to play before you get logged out)

PC made accounts (ie, made via the website) can play on any device, but require a full sub to play after the initial 8 hour trial has expired.