You can remember the meaning of 十二 with this easy mnemonic:
At <strong>10</strong> (十) pm the <strong>two</strong> (二) of us met up to celebrate a promotion. In no time, it was <strong>twelve</strong> and we both had to call it a night because of work the next day.
Using mnemonics to remember the meaning of Chinese characters like can have an enormous impact on how long to learn Mandarin it takes.