Should I provide you with the exact date of my arrival?

The answer is no, since you are able to estimate it. Nevertheless, we kindly advise you need to choose a date which is earlier than the arrival date as you planned. The reason is that you are only allowed to enter Vietnam later than the date stated in your approval letter; on the other hand, you are required to pay extra fee for visa re-processing.

For instance:  If you apply for a 1 month visa and submit your arrival date as Jan 01, 2016 that means your visa letter will be valid from Jan 01, 2016 to Feb 01, 2016. Therefore, you can arrive in Vietnam during this period of time but have to leave the country by Feb 01, 2016.