The beginning of the action occurs in 1966 as mentioned at one point. It is also mentioned nobody can notice how fast time flies, so we don't know when the movie ends. However there is a hint: a Nazi official arrives towards the end. Since he has building models he must be an architect and since he settles in a suite he must be high ranking: it could be Albert Speer who died in 1981. Hence 15 years might have elapsed since the beginning of the movie.