in是指在...之內(nèi)，所以不難理解in time可以是指提前完成某事，是及時(shí)；on則是指在某一時(shí)間點(diǎn)上，是個(gè)確切的時(shí)間點(diǎn)，所以on time是指準(zhǔn)時(shí)。

Tom managed to get to the airport in time.

湯姆設(shè)法及時(shí)趕到了機(jī)場。

There's a slight chance that he'll be back in time.

他及時(shí)趕回來的可能性不大。

I hope we get there in time.

我希翼我們及時(shí)到達(dá)那里。

You should return the book in time.

你應(yīng)該及時(shí)還書。

It's good to go to school on time.

按時(shí)上學(xué)是好的。

She always pays her bills on time.

她總是按時(shí)支付賬單。

We worked like crazy to get it done on time.

我們拼命地干，好按時(shí)完成這項(xiàng)工作。

The bus came right on time.

公共汽車正好準(zhǔn)時(shí)到達(dá)。

來源：高三網(wǎng)