Important Precipitation Composite info
These maps of NEXRAD estimated storm accumulated precipitation are created by compositing the NEXRAD Level 3 storm total precip product (NTP) from many different radar sites. Each radar site defines the time range of accumulation as "since the last time this radar switched from clear air mode to precipitation mode," thus the time range of accumulation varies for each site.
As each NEXRAD site will have a different time range, it doesn't really make sense to attribute a time range to the composites, since any time range wouldn't apply to the entire picture. The composites can give an idea on how much radar estimated precipitation has fallen over a region, but be aware that the time range for each contributing NEXRAD site varies.
The National Weather service plots of Storm Total Precipitation do include the start and end times for the accumulated precip for each radar site (on the right side, right above the image,) so those could be consulted to help make sense of the values seen in the composites.
Here are direct links for several NEXRAD locations near Madison - other locations can be chosen at https://radar.weather.gov
Milwaukee/Sullivan, WILa Crosse, WI
Green Bay, WI
Chicago, IL
Quad Cities, IA
Minneapolis, MN