I am licensed in Nevada, but this Answer should apply in Wisconsin.
It is the date of the accident and not the filing of the report that starts the Statute of Limitations running. Having checked the law ( http://www.legis.state.wi.us/statutes/Stat0893.pdf ), it appears the Statute of Limitations is 3 years for personal injuries (893.54) and 6 years for property damages (893.52).
If you have an injury, then generally you would have 3 years from the day of the accident to file suit. If you are not hurt and just have property damage, you would have 6 years from the day of the accident to file suit. The time period starts to run from the day of the accident, not from the filing of the accident report.