Depends on the average or typical climate you will be at. 100% cotton is great for the desert in the day time.
For fairly dry climates, but not quite desert like, 35% is fine. Where i live
(VA), it tends to be moderately to very humid much of the time, and 35% cotton could be on the border of possibly a bit too much.
Also, check out Richard Nisley's research on this issue, he found it was more the thinness and weave of a garment which most affected a garment's drying time, over specific material. With that said, an all synthetic shirt with the same weave and thickness as an all cotton shirt will dry faster than the all cotton one, but if both are sufficiently thin, the cotton will dry fairly quick.
The difference is is that cotton doesn't insulate when wet, whereas polyester does some. However, while that may be bad in cold temps, it's actually a nice thing in warm to hot temps.
I would also suggest looking at other blends too. Linen or hemp mixed with polyester is great. As is tencel with predominant polyester or nylon. Linen/hemp and tencel seem to dry noticeably faster than cotton, yet are still absorbing and cool/conductive materials. They also have better odor reduction properties than cotton (especially linen and hemp).
So a shirt with slight majority of synthetic to linen, hemp, or tencel is a really nice combo for warm to hot weather. If it's really humid, and really hot, definitely want more synthetic to natural blend ratio.
I have a shirt made with 65% polyester and 35% linen. It surprised me at how well it minimized odor--i thought with all that polyester it would get stinky somewhat fast. Nope, though not as good as 100% linen. Also feels dry really fast even in humid VA weather.