The hefsek taharah must be performed before sunset (sh'kiah) in order to begin counting the clean days the next day. If your moch was inserted before sunset and you rotated it so that it entered the folds of the vagina (as opposed to just inserting it without rotating), you may count your moch as a hefsek. However, if it was not rotated, or if it was inserted after sh'kiah, it is not valid and you need to perform a new hefsek this afternoon.

In a case where a woman performed a valid hefsek after sh'kiah, and then forgot to perform a new hefsek the following day, the first hefsek can be counted for the following day. For example, a woman did a hefsek on Tuesday night after sunset. She forgot to perform a new hefsek on Wednesday afternoon. She can begin to count her clean days on Thursday, based on the Tuesday night hefsek. Her mikveh night will be the following Wednesday night.

Please feel free to get back to us with any further questions.