It's high, but as long as you have strong vesting in place, why not? If you feel like this could work out great, the long-term split is not completely wrong (50/30).
However, I do see a bunch of red flags. You seem to need a developer, not a title-inflated CTO. You may need someone who has some serious time to focus on this since your deadline (February) is so close. Your potential CTO is part-time, so there is huge risk there.
Is that CTO a doer, or will he write specs and expect to find someone else to do the dirty work?
Worst case, you get rid of him after 6 months, that will have cost you 4% of equity. Would that be acceptable to you? And to him?
EDIT: hint to the community. My answer currently sits at "-1", which means: please go away, your anwers are not welcome here. Are you sure going negative is the best way to grow a positive community?
What's your cost to get rid of the CTO and replace them? Value it and compare it with what they are asking. Pick the path that is the least expensive. Simple.