现在我不会唱歌了，但我年轻的时候会。
I can't sing now, but I could when I was young.

我已经写了三个小时了。
I've been writing for three hours.

时间就是金钱。
Time is money.

"when" 是一个时间连接词。
"When" is a temporal conjunction.

水被加热时，可以变成水蒸汽。
Water can be changed into vapor when heated.

你什么时候付清最后一期分期贷款？
When will you pay the last installment of the loan?

时间差不多了／是时候了。
It's about time.

什么时候能准备好？
When will it be ready?