I'd say at least a good 27 hours, depending on your tolerance.
Expect a nasty mother of a body load I'd gather. I'd rather take an amphetamine with 2c-I than a doxx (if someone put a gun to my head and gave me a choice, either chemical on their own is sufficient enough for a plus 4 if you've got the right mindset perhaps some ketamine or dmt handy).
I'd have a seriously reliable stash of benzodiazapines for when you finally want it to end and go to bed, and for the overstimulation both of those would cause.
If you must mix these two classes why not 2C-C and DOC? The chlorine atom of the series seems to be much more forgiving than the Iodine.
Also, I'd take them both at the same time, unless you want to awake for 3 days. Just my 2c.