Summary:
-If fireball+pyroblast is your opener on crystal (aka not scorching it to build stacks), ignite's initial timer is set to 5.0 then 6.0 (or 5.9) immediately.
-Did some range testing:
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It's also possible to get 0 seconds between your fireball cast and ignite proc
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Note: Above tests were done by creating a 10 second duration weakaura that procs when Fireball is 'cast' in combat logs, and when ignite is 'cast' on the mob and subtracting the difference to determine travel time
This should mean we can reliably get ~6.6 seconds of ignite for combustion correct? Superchinese while running in from 20 yards means it takes 0.7 seconds to travel to boss to start ignite, ignite hits and it set to 5.0 then 5.9 immediately.
At a minimum that should mean we should be able to get all of superchinese in during lust
Edit: I also made a video for anyone who wants to learn/show others how to do fire opener.
https://www.twitch.tv/searix/v/66860720" target="_blank