These buckets are also dynamic and constantly adjusting. So if you were looking at D2, then if you leave it a short time, or maybe a long time, it may come back as D1 or even D3. Now the uncertainty isn't helpful, and I'm not entirely convinced the switching PCs is going to help either, given the way that availability gets pulled from Amadeus / Pegasus. So what I would do is book the first two tickets at D, buy the next ticket at (presumably) the higher R cost, maybe leaving it 20 minutes or so. Use the Hold fare button if it is offered, but then cancel / rebook, given the 24 to 72 hour time frames for doing this should the cheaper fare re-appear.