Count a specific event occurring within the same minute for 5 or more than 5 times

Count a specific event occurring within the same minute for 5 or more than
5 times

Let's say I have column A which has the word "Client rebooted" and "lockup".
I have another column B which gives me the date and time rounded off to
the nearest minute of the corresponding events (i.e "client rebooted" or
"lockup").
I am trying to figure out a way to count the word "Client rebooted"
occurring 5 or more times within the exact same minute of the same day.
Does anyone know a way to do this?