question?how long do i have to dispute a transaction

I just found out our in home nanny may have been using my debit card without authorization.  How long do i have to dispute transactions.  I am going to request statements for the entirety of her stay with us but I am having a hard time finding information on the timeline in which disputes must be filed.

Admittedly I did not monitor the account she allegedly misused as much as I should have. A police report has been filed.