i use netflix by web
the mail service uses 'post office'
going on memory, its about 3 days to get or return a movie
how many movies you can have at a time depends on the level of service you are subscribing to
if your service level is '1' movie then , it must be returned before the next one in your cue is sent out
If you make a cue list
the next movie in your cue is automatically sent out when a movie is returned/received
with a '1' movie service level, you could expect a new movie approx every six days
with a higher service level you could have 3 movies 'maybe more' at a time
as you as you watch one , drop the return in the mail , by the time you got to number '3' , new ones from your cuee would already be arriving