Do timing issues happen during list building as well ( proverbial chicken and egg ) ?.. Is it possible to take a Saber Squadron Interceptor ( Pilot 4 ) then add the Veteran Instincts elite talent ( Pilot 6 ) thus unlocking the Royal Guard TIE modification pre-requisite ( Pilot 5+ ) ???

Yes, but you should never do that, ever.

Suppose I should elaborate.

Common sense:
Saber = 21 pts. Take VI, bump it to 22. It's now ps6 and can equip the RG title but you've filled his elite skill slot with VI.

Royal Guard Pilot = 22 points, ps6. For 1 point more (the same cost as equipping VI), you get the +2 pilot skill, you can equip the RG title, and you still have your elite skill slot free to take whatever. (Ok, to take PTL, let's be honest.)

In other words, if you put VI on Saber, you're just making a nerfed version of the Royal Guard Pilot that title was designed for, which makes absolutely no sense to do, ever.

Just use the Royal Guard Pilot instead. Same cost but keep the Elite Pilot slot open.

If you have the Royal Guard title then you should also have the Royal Guard pilot.

Yeah, just noticed the Royal Guard Pilot vs Saber Squadron Pilot issue on an online list builder :-) thanks for the reply. At the least, it helps to know for other ( future ) prereq matters that this does work.

The modified values kick in the instant the card is argued - put VI on someone and they are placed during setup with their new, increased pilot skill.

The example we always used when figuring this stuff out was the Slave-1 title. It adds the torpedo icon to your upgrade bar, right? If that doesn't take effect the moment the title is added - well before set-up, it wouldn't work. The only way it works is if the title instantly adds the torpedo upgrade option while you're still building your list, long before it gets plunked down on the table. And that sets a pretty clear precedent how other upgrade cards work.

I honestly think considering any sort of timing during squad construction is overkill. What's the timing if I add Wedge to my squad and realize it puts me 3 points over? How long is my squad illegal, and what happens during that time?

Your squad has to pass a validation check which ensures it meets all rules when the game starts. So long as it all adds up at that moment in time, it's all good.