Don't think there will be much Wimbledon on ZDF. In the afternoon, ZDF is probably focusing too much on news, press conferences, reportages from UEFA EURO 2004, so I think they won't show Wimbledon.
ARD will show Wimbledon, but only about two hours and you will miss about one hour until you can switch over to DSF
Anyway, both channels are channels for old people and both channels don't like tennis and don't pay much attention to it and prefer broadcasting programmes for retired people.
They are both pathetic, and ZDF and ARD will never show Wimbledon on the same day together, at most they are are alternating between each other: 1st day ARD, 2nd ZDF, 3rd ARD... like, for example, it was during the French Open. But for Wimbledon, I guess, only ARD will show tennis; every day, but only for about two hours.