Transferring my answer to this thread:
I personally think you have to choose. I think for sponsored magic you have the the flexibility of choice. You can choose the bonus to apply to an evocation but then you have to decide the usual stuff like power/control, defense/offense or you can choose to apply it to thaum, but then that's it. It kind of feels like double-dipping(actually triple or quadrupal dipping) if it can apply to everything at once.
And actually, if he took the evocation foci(from the evocation power) and applied them to the element "chronomancy" then he could have that bonus, but I don't see those evocation foci crossing over to a thaumaturgical application. And the only reason he can do that is because has sponsored magic otherwise that element wouldn't be available to him.
So, in my mind, I can see there being a +4 chronomancy evo-thaum attack for the reasons I just mentionned, but he'd have to choose offense/defense and he couldn't apply them to actual Thaumaturgy.