| makeresults | eval Event_Reported_Time="7/21/2016" | eval Comment_Date="7/22/2016" | eval Event_Reported_Time = strptime(Event_Reported_Time,"%m/%d/%Y") | eval Comment_Date = strptime(Comment_Date,"%m/%d/%Y") | eval diff_time = Comment_Date - Event_Reported_Time | eval diff_days = diff_time / 86400
Like this:
... | foreach * [eval <<FIELD>>_Epoch = strptime(<<FIELD>>, "%m/%d/%Y")]
| eval Diff = (Comment_Date_Epoch - Event_Reported_Time_Epoch) / (60*60*24)