A woman told her husband that she was scheduled to go to the mikvah on Thursday night. However she would like to surprise her husband and go a night earlier (on Wednesday night). All her bedikas are good for Wednesday night. My question is can a woman tell her husband that she is going to the mikvah a day later and surprise her husband a day before.
Before deaing with the actual question, if she indeed made all of her required bedikos and seven days have passed, why did she start coiunting a day early? Did she indeed do the hefsek at the end of day 5, or did she make it earlier? If she indeed waited 5 days and she is playing a trick on him, that is problematic, and she should not play such games. If she wants to surprise him, she should find some other way to do it. When she told her husband that she was scheduled to go to the mikvah only on Thursday night, that means that she essentialy told her husband that she will be tameh until then. Then when she “surprises” him, she essentially is changing from what she originanlly told him. The Shulchan Aruch says that a woman that does something like this is not believed to change her story, that now she is indeed tehora, and is considered to still be temeiah. There are poskim who say that she may be tehora, but she should be chastised for doing something like that. In any event, everyone agrees that she should not do something like this.
Shulchan Aruch Y:D 185-3, Shach ibid 2, Gra”z ibid 4, Chut Shani ibid 7-1, Shiurei Shevet Halevi ibid 2-1.