As soon as you know you will need an extension, immediately begin preparing your letter. You need to give the recipient as much time as possible to make a decision about your situation. You also want to appear prepared, despite asking for an adjustment to the schedule. Consider all factors and submit a realistic request. If you ask for too little time, you may need to request another extension. Missing deadlines should be avoided whenever possible. So, it’s best to overestimate a little.  Depending on the situation, you might need to consider your letter as part of an ongoing negotiation. In that sense, it is better to ask for a longer amount of time so that you can compromise and meet in the middle.  Gauge your pace based upon your current progress and what parts of the project have yet to be completed. For example, if you have worked on a consulting project for three months you should have a pretty good sense of how much is left to do. Be aware of the time constraints facing the recipient as well. They may be under their own deadlines that will now need to be pushed back. For example, college professors are often required to submit midterm grades and schedule their paper deadlines accordingly. Verify the current deadline before you ask for it to be altered. You don’t want to appear disorganized by requesting an extension when you don’t understand the current situation. For example, some government entities require that you submit your request within 24 hours of initial contact with them. If this doesn’t work for you, then you can always cite the tight turn-around schedule. You are taking the time to craft the letter and your recipient will then take the time to read it, so make it worthwhile. Carefully consider your true reason for needing the extension and honestly convey this to your reader. Don’t lie or exaggerate as this will only hurt your case.  A good reason might be the desire to be thorough or cautious in your work. For instance, if you are completing a project that could potentially impact the...

How would you rephrase that briefly using Vietnamese?
Viết thư càng sớm càng tốt. Xác định thời gian bạn cần thêm là bao lâu. Chú ý về luật lệ hiện hành. Đưa ra lời giải thích hợp lý. Nêu ra một vài chi tiết được chọn lọc cẩn thận. Giữ văn phong và nội dung tích cực. Đọc lại thư trước khi gửi.