How much time it will take to write a test in Appium?

It totally depends on the test which is to be performed. If the test simply runs a scenario, it will take commands of very few lines and also very less interaction will be needed in order to test that application whereas if the test is complex and requires transfer of data it will take much more time than the previous one and also it will be a little difficult to read the lines of code of that test. 

This discussion can be concluded by saying that there is only one factor on which the time needed depends which is the complexity of the test and it is directly proportional to the time taken in Appium.