是要等12個月

"You must be free from immigration time restrictions when you apply for naturalisation. Unless you are married to or the civil partner of a British citizen, you should have been free from immigration time restrictions during the last 12 months of the residential qualifying period."

http://www.ukba.homeoffice.gov.uk/britishcitizenship/eligibility/naturalisation/standardrequirements/

還有一些遺雜要求，可是應該都是樓主相當然就滿足的。

入籍需要多長時間處理就要看運氣了。最短幾周，最長半年。我做的時候一個半月就批下來了，辦護照也比較快。