Inscription Question

Hi, I have a noobish question regarding adding inscriptions to items. I recently found a Req9 gold Adept Conjuring staff, which has effects of:

HSR 20%
Energy + 10
11-22 Earth Damage
HCT Spawning magic 20%
Insc 'Show me the Money'

What I would like to know is, if I were to change the insc to an Aptitude not Attitude inscription, would the 2 x HCT Spawning magic 20% stack?

Thanks in advance

Both upgrades are triggered separately, which means you'll have an 4% chance that both upgrade will trigger (quartered cast time), a 32% chance that exactly one upgrade will trigger (halved casting time) and a 64% chance that none of the upgrades will trigger (normal casting time).

There was recently a patch that changed how much the activation time could be speeded up, if I'm up to date the actual effect of both upgrades are: 36% of halved casting time, 64% chance of normal casting time.

In other words, yes, they stack.

Yes you will have a 36% chance of HCT (20% for the first mod to trigger + 16% (20% of the remaining 80%) for the second mod to trigger if the first mod doesn't trigger = 36% total chance).

Previously, you'd have a 4% (20% of the first 20% triggering to trigger the second mod as well) chance to HCT twice, effectively quartering your cast time (leaving a 32% single HCT), but this has been nerfed, resulting in the full 36% only triggering once.