It's kinda implied on the title of the feat though, just like the one for larfleeze during the Christmas seasonal, iirc it had days on the title too.
I just found Batwoman about 7 times and then checked and it says 1/13. The next time I went right up next to her till she left, it is still 1/13. I'm not sure what I did once that I'm not still doing
Did you find Batwoman 7 times in one day or once in 7 days? Because it is counted only once a day, in the end you need 13 days to complete this feat.