IV is a 3 min CD. FO is a 1 min CD. FO should be up whenever IV gets off CD. What would the delaying be?
In general, besides syncing FO with PC, you don't want to delay CDs to stack them. The only exception would be if you know the fight length and only get 1 more use out of a CD, then you could delay it to use with another CD since the delay won't cost you another use. That would require a good knowledge of the fight and your usual kill times though, and its a pretty small increase.
Delaying FO is not really something uncommon, while the boss/mob are moving you don't want to FO, you also want to keep FO for burst phase.
On imperator for example FO almost always comes out of CD when Imperator is levitating (between P1 -P2) I don't want to FO there because the boss will me moved to the center of the room.
I also want to keep my orb for the Interval between P2 and P3, so I'll delay it this time too (hopefully IV will come out of CD during that interval or slightly before).
There are a lot of time where FO will be off sync with IV, btw i never delay it too much if I see FO will come off CD in less than 20 s I'll IV right away (with WJ you can at least extand by 4 s and i may use a IL without FOF during movement) .
I think the question can be asked, how much can we delay IV for FO? Is it worth to IV without FO with TV?