Tourist visa is usually valid for 6 months starting the day you receive it
Unless you are a citizens from specific countries including Finland, Japan, New Zealand, Luxembourg, Singapore, Cambodia, Vietnam, Laos, Myanmar, Indonesia and Philippines, where you may get a tourist visa on arrival or TOVA, you will need to arrange your visa in advance. The tourist visa is usually valid for 6 months starting the day you receive it as opposed to the day you enter the country. The process usually take a couple of day, but on some special occasion can take a couple of weeks, so it is better to plan in advance. Moreover, as the cost is the same, it is preferable to ask for a multiple entry visa, to give you the flexibility to go back and forth to the country.