Should I provide you with the exact date of arrival?

No, tt is not necessary. The arrival date should be the earliest date you plan to arrive, but you can arrive after that date. The departure date is the last day you are permitted to be in Vietnam, unless you get a visa extension or take the flight to Phu Quoc island where Vietnam visa is exempt for 15 days.

For example: If you apply for a 1-month visa and submit your arrival date as Jan 1, 2017, the visa letter will be valid from Jan 1, 2017 –  Feb 1, 2017. You can arrive anytime between Jan 1 - Feb 1 but must leave the country by Feb 1, 2017."

Note: The approval letter can not be amended once it is issued, so in case you wish to arrive earlier than the date written on the approval letter. You are required to apply for a new letter of approval to update the date of arrival.