Let's do some fairly straightforward math.
Dakini/Athame (OAT)= 195/211
/NIN = 20% delay reduction. 406*.8=324.8 rounded up to 325.
Assuming we have 22% gear Haste (Turban, Rapparee, Dusk Gloves, Desultor Tassets, Dusk Ledelsens +1, Swift Belt). Also assuming we have Marchx2, Haste, and unmeritted Haste Samba.
62% Haste. (1-634/1024)*325 = 123.5, truncated to
124 delay.
Now let's just assume we had fully meritted Haste Samba.
62%+5%=67% Haste. (1-686/1024)*325 = 107.25, truncated to
108 delay.
Now we take the unmeritted delay versus the meritted delay to find out how essential this merit is for a DNC to correctly function.
124/108=1.148, truncated to 15%. capping your Haste Samba in this situation will be a 15% increase to your DoT and WS frequency.