If you used the bathroom but you're not in the right state to say Asher Yatzar (about to take a shower or not properly dressed). What should you do?
As @DanF comments "you need to be clothed and outside the bathroom".
Rabbi Ari Enkin has an extensive discussion of how much time you have.
The main opinions that he quotes are shortened below (see the article for references)
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 and 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 merely recite it once in the morning.
A number of authorities rule likewise and assert unequivocally that asher yatzar is not subject to any deadline or time limit.
Opinions as to the time limit vary from thirty minutes to a seventy-two minutes.
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.