That's exactly the question I wanted to ask! So is a significant portion of your time spent programming? Do YC startups measure this?
I find that if I code in a Blub language I spend 4 hours coding, but in a non Blub language I spend 2 hours thinking and 1 hour coding.
So according to your stats you get a 25% improvement in productivity by using non-Blub language (don't worry as you gain familiarity with non-Blub programming this will actually improve) and that means launching a month earlier.
The only reason to not use a non-Blub language is that you need to write in the Lowest Common Denominator of your team and if the entire team isn't comfortable in a specific language you'd better not use it.
The only exception to the above rule is if you separate your efforts in a very specific way, if instead of using the entire team to build project A, you use part of the team to build tools that help build projects like project A easily and the rest of the team uses the tools the other half created to actually build project A. In which case the tool building group can use more powerful languages without any adverse effects.