By: Rabbi Ari Enkin
As a general rule, asher yatzar, the blessing recited after one relieves oneself, must be recited immediately once one has washed one’s hands after using the washroom. There is some discussion; however, as to how long one actually has to recite asher yatzar in the event that for whatever reason it was not recited promptly after relieving oneself.
According to some authorities there is actually no set time limit. The Levush discusses a situation in which one went to the washroom in the middle of the night but did not recite asher yatzar at the time due to an inability to wash one’s hands. The Levush rules that the asher yatzar can be recited in the morning even if one does not relieve oneself again upon awakening. Similarly, there are those who rule that one who goes to the bathroom several times during the night need not recite asher yatzar each time and need merely recite it once in the morning. Again, this is true even if one does not relieve oneself upon awakening. Indeed, a number of authorities rule likewise and assert unequivocally that asher yatzar is not subject to any deadline or time limit. There is even a view that one who forgot to recite asher yatzar after relieving oneself and then remembers the omission after relieving oneself again some time later is to recite asher yatzar twice, one after the other. However, the halacha is not in accordance with this view.
Other authorities disagree and argue that if Birkat Hamazon, which is d’oraisa, has a time limit (generally assumed to be seventy-two minutes or until the food is digested) then certainly asher yatzar must have a time limit, as well. Opinions as to such a time limit vary from a thirty minute deadline ranging to those who suggest a seventy-two minute deadline. The most widely accepted opinion on the matter is that one may recite asher yatzar up until one feels the urge to relieve oneself anew. One who relieves himself at the very end of a meal should recite asher yatzar before reciting Birkat Hamazon or any other bracha achrona.
There is some discussion whether or not asher yatzar should be recited by one who is suffering from a stomach condition or is otherwise relieving oneself repeatedly. According some authorities, if one knows that one will end up back in the washroom in a short while due to the condition, then asher yatzar should not be recited. Others rule that as long as one feels relieved then asher yatzar is to be recited each time regardless of any other considerations.
 Levush, OC 4:1  Rivevot Ephraim 6:123:2.  Elya Rabba (Zuta) 4:1; Kitzur Shulchan Aruch 196:3; Mishna Berura 7:1.  OC 7:3.  Mishna Berura 7:6  Darkei Moshe, OC 184; Taz, OC 184:2; Mishna Berura 184:20; Be’er Moshe 3:39:16.  OC 184:5; Mishna Berura 184:17.  Birkei Yosef 6:3  Kaf Hachaim, 7:7; Tzitz Eliezer 11:45:6.  Yechaveh Da’at 4:5; Yabia Omer 8:22; Rivevot Ephraim 1:50:3, 7:30, 8:2. See also Be’er Moshe 2:10:2 and Chayei Moshe 7:3.  Mishna Berura 7:1; Yabia Omer 8:22.  Mishna Berura 7:2; Kaf Hachaim 7:1.  Asher Avraham, OC 7; Kol Eliyahu 2:1; Be’er Moshe 4:5; Yabia Omer 9:2.  Mishna Berura 7:2; Kaf Hachaim 4:1