Originally Posted by
javabytes
1. Yes, it matters. Upgrade priority is by elite level, then fare class, then Reserve card, then time of request. If you split the PNR 8 days out, your request will be dated then, as opposed to getting a bit of a boost by having done it 60 days out. Granted this is the 4th level tiebreaker, so the effect is probably only a couple slots at most, but it could make the difference.
2. Ask the agent to "link" your PNRs after splitting them. This is really just a note that you are traveling together, but it's as much as you can do with split PNRs. An agent who sees the note should try to reroute you and your companion together in the event of IROPS, but there are no guarantees.
3. The seats will "hold" but they will not be able to change to other EC or preferred seats, or to reselect them if there is an equipment swap and they are automatically reseated in standard seats. Some agents will seat your companion next to you in EC or preferred seats, but recently this seems to be limited to a spouse, not just any companion.
javabytes is correct.
In the OP's situation, I recommend splitting somewhere like 10 days out. As noted, the time of request is the fourth time-breaker. That's EXTREMELY unlikely to make a difference in whether the OP gets or does not get an upgrade.
Less than two weeks out is also unlikely to have an equipment change killing the EC seat selection for the non-elite status partner.
Whether or not the OP should split a reservation also depends on the length of domestic segments -- ATL to MIA, probably not. SEA-ATL, hell yes.
As for linking a reservation -- mostly useless and unnecessary. Wife travels with me on a separate PNR. We've been IRROP re-routed separately, and bump offered to me but not wife. In each case, I've able to say, "Hey wait a second! I have a traveling companion with me!" Where a linked reservation is useful (in the sense of "better than nothing") is with children or inexperienced travelers who can't assert their requirements when things go wrong.