Something like that

Let's say:

You book the itinerary today
with the first flight in 300 days
and the last flight in 330 days (note 1)

Then during the intervening time you can move these dates out further into the future and finish up with
The first flight one year from today (note 2)
and the last flight one year after that

Note 1: you would likely want to have a (short) stopover between flights, rather than transits. This is because later changing a transit to a stopover is considered a re-route and so attracts the USD125 change fee

Note 2: There is a risk to changing the first flight of the itinerary - which is that if the fare has increased since you purchased the ticket, then you have to pay the new fare. This is also the case if you re-route any part of the itinerary before taking the first flight.