No, it is NOT necessary. The arrival date you provide should be the earliest you plan to arrive, but you can totally arrive after that date. The departure date is the last day you are permitted to be in the country, unless you get a visa extension.
Note: The approval letter can not be amended once it is issued, so in case you wish to arrive earlier than the date stated on the approval letter. You are required to apply for a new letter of approval in order to update the date of arrival.