Here's something you don't understand about holding buffs. You NEVER hold buffs in the opener. They are aligned for a reason. The ONLY time you hold buffs is depending on your kill time. For example, in my static we have DNC, DRG, MNK, SMN, SCH. So depending on the kill time of the boss you would hold the final 2 minute window for the final 3 minute window to end the fight under maximum buffs or anything to that extent. Holding buffs is something you do towards the end of the fight, never in the beginning when the openers set the pace for the entire rest of the fight and pretty much EVERY job needs their opener to start and end at a certain time (for example WAR, after Storm's Eye, they are either doing IC > IC > IR or IC > IR > IC, no exceptions so that they stay aligned with Brotherhood (if it exists) and also stays aligned for Trick Attack (and Technical Step) etc.

So, let's use Voidwalker for example since he's a 0 downtime fight pretty much. Let's say your group kills it at like 9:17 or so. Using this timing you could delay final Technical Step, Chain Strat, Dragon Sight, and any other 2 minute CD for the 9 minute window so that everyone is under the effect of as many buffs as possible when the fight ends.

tl;dr holding buffs is an end of fight optimization/speed run optimization, not a beginning of the fight optimization. Openers are already optimized, do not mess with them.