Im having some issues with 2 things, and would appreciate it if someone could clear things up.

(1)

Ive read that the mean of "the sampling distribution of means" is the same as the "populations" mean.

To construct the sampling distribution of means, i need to take X * number of independent samples (where each sample is composed of >= ~30 observations) from the population, calculate the mean of each sample and plot the mean.

Whats the minimum value that X (the number of means used to construct the sampling distribution) should be, or do you typically plot the distribution and increase X until it begins to look normal?

(2) If i record the time between planes landing, and have 250 observations, are those 250 observations my "population", or does the term "population" refer to all the values, ie if i had sat there till the end of time recording?

Thanks for your time.