The answer is NO. You just can arrive on any day AFTER the arrival date specified in your official visa and your visa approval letter. You are advised to file for a fresh visa acceptance letter if your plans change, and you want to visit Vietnam before the designated arrival date.
You can find more detailed answers at Should I provide you with the exact date of arrival?
The Vietnam eVisa is a recent category of visa introduced by the Vietnamese government, aimed at expediting the visa application procedure and bolstering Vietnam's tourism sector. Nationals from qualifying nations can utilize these visas to journey to Vietnam for tourism, visiting family, friends, or standard business engagements. Travelers with intentions other than tourism or business meetings should approach the nearest Vietnamese embassy in their respective home country to pursue a conventional visa application.
The e-visa for Vietnam can be obtained online via the Vietnam Immigration Services website. The procedure usually includes completing an online application form, providing the necessary paperwork, and making the visa payment electronically.
Once the application is accepted, the e-visa will be digitally associated with your passport. You can enter Vietnam through 8 authorized airports and land border crossings with a valid e-visa. The Vietnam eVisa remains effective for a duration of 30 days, commencing from the date indicated on your approved eVisa document. During this validity timeframe, you are free to enter Vietnam on any date. This single-entry visa permits a stay of up to 30 days once you're in Vietnam.