based on my expereice a couple of months ago,
1. 一般從收到這個通知到interview的appointment 之間的間隔有多久?會不會至少在一個月以上?
one month
2. 這個interview 可不可以提前去?
No, you could reschudle it, but only choose a later date. I was not successful in changing the date because it is very complicated, you have to call them which will take for ever to talk to a humanbeing, and the guy usually know nothing about reschdualing
3. 副申請人的case是必須在主申請人的case批了之後才會批地嗎? 和主申請人的 case分開會不會影響case的批準呢?
It is usually the case, but depend on your luck, I was told that my NC is not clear and have to wait for ever.