You never never never delay mind blast. Ever. This is our main orb generator and we never delay creating orbs.
This is most common misconception about Dotweaving. Since every Dotweave rotation is based on exactly described Global Cooldowns happening one after another in a strict order, each single "MFI" in such description means one single Gloobal Cooldown, which - in case of MFI - lasts for 2 ticks of Insanity, not full 4 ticks, because full Insanity cast lasts for 2 consecutive Global Cooldowns, each of them consisting of 2 ticks.
Also, which is not apparently obvious for every shadow priest, you WILL need casting bar that shows real amount of 4 ticks, preferably with latency delay. so that you know exactly when to clip/stop casting Insanity after second tick. I've recently spoken to a shadow priest using ElvUI and its default casting bar that showed... 3 insanity ticks on 100 level. Get Gnosis for ticks.