NATLANG: High German Consonant Shift

Right now, I'm making a heavily High-German-influenced language,
currently under the pseudonym of 'Latinesque'(I've made it once before,
and am now redoing it, because the other one was not nearly
realistic/rigorous enough).   I'm not sure whether the name will stick
or not.  Anyway, I'm trying to come up with a background history to go
with the language, as I find the current I little lacking.

Basically, I need some estimated dates for the High-German consonant
shift.  Within a century should do fine.

Thanks.