I know there is a deadline for brochois after a meal (until hungry again, 72 min). But if one did not say Asher yatzar, for how much time can one say it?
What are the sources on this subject?
There are many opinions ranging from 30 minutes to 72 minutes to until one has the need to relieve oneself again.
From Halachipedia
From R Ari Enkin (see there for sources)
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.
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.