A bedikat hefsek taharah may be performed right after washing, internal or external.
When a woman cleans herself internally (as is desirable before a hefsek taharah), waiting around ten minutes may be healthier, since it allows time for some of the natural lubrication to return to the area, reducing the chance of irritation to the vaginal lining. Halachically, there may be some preference to wait a few minutes after internal washing, so that new bleeding will show up on the bedikah. But there is no halachic requirement to wait at all between even internal washing and the hefsek taharah.