visa expiration

Is the visa valid starting from the Issue Date or from the date I enter Vietnam, which is also the date I put on the application form? I am afraid of applying too early. Visas in some countryies say they are valid from the Issue date, that means if I apply too early,let say 2 months before my planned trip, and if I apply for a 30-day visa for a ten-day stay, by the time I get there, my visa might expire. Thanks!