While traditionally flights were cheaper when booked round trip and 21 days in advance, those requirements are often no longer required. I just did a month long search on ITA for one way flights from New York to Los Angeles. There are plenty of tickets for next Saturday (7 days from now) for $130. The round trip price is simply the two one way tickets added together.
Within the next 7 days, the price increases but not by much. You can travel anytime before Saturday for only $284 one way. Obviously if you want a refundable/changeable ticket the price is more expensive.
While this is only one example (and a domestic USA itinerary only) the point is that the days of requiring a round trip, with a Saturday night stay and 14 or 21 day advanced purchase are often no longer required.
Yes, it doubles at 6 days and under, but my point is, it's neither 14 days nor 21 days for pre purchase, and no round trip is required. The "old" thinking about fares is no longer valid.
Within the next 7 days, the price increases but not by much. You can travel anytime before Saturday for only $284 one way. Obviously if you want a refundable/changeable ticket the price is more expensive.
While this is only one example (and a domestic USA itinerary only) the point is that the days of requiring a round trip, with a Saturday night stay and 14 or 21 day advanced purchase are often no longer required.