I know I posted this before, but it didn't get seen.
These are the testing times for the main counties of Michigan:
All these counties test on the first Saturday of the month at 1:00 PM! (unless says otherwise)
Ingham:
all year (High success)
Eaton:
all year (High success)
Oakland:
March - Nov. (unknown)
Washtenaw:
March - Oct. (unknown)
Jackson:
all year (high success)
Wayne:
all year (high success)
Macomb:
all year (unknown)
Kent:
April - Oct. - 12:00 PM (high success)
Kalamazoo:
April - Sep. (unknown)
Calhoun:
all year (unknown)
Bay:
First Wednesday of every month at 1:00 PM & 7:00 PM (high success)
Saginaw:
First Wednesday of every month at 12:00 PM (high success)
Grand Traverse:
uses CodeRED (Some towns may sill test sirens)
That's all of the mostly populated counties in Michigan.
It's safe to say that the rest of the counties will test on the first Saturday of the month around 1:00 PM, with a low success probability to be safe.