Speed-ups

[Synjin Zaic]

Are you using them as you get them or saving them for later in the game when the upgrade time gets very long. (I’m still at the 8-12 hr upgrade range with some now hitting 1 day) I have 74 - 1hr. and 13 - 6hr.

 

[Exiliado]

I save Speed Ups for discount events when I want to squeeze in as many cheaper upgrades as possible.

 

[No Angel]

In higher age when we still have to actively upgrade, yes I save them, for same reason with Exiliado.
But in younger age, you might want to advance as quick as possible (since you have the game basics already), so use them for crucial upgrades, like the war academy, mercenary camp, and castle upgrades.