I'm afraid I have to remind you that time is up.恐怕我得提醒你时间到了。

1.Remember about it.别忘了这件事。2. Don't forget to post the letter.别忘了寄信。3. You haven't forgot about it, have you?你还记得这件事，对不对？4. May I remind you to help her with her report?请允许我提醒您帮她完成报告这件事。