If you forgot to say Asher Yotzar and remember a while later, is there a time limit as to when you are allowed to say it?
The Shulchan Aruch O.C. 7:3 says that a person who went to the bathroom a second time after forgetting to say Asher Yatzar the first time must say Asher Yatzar twice.
The Mishna Berura 7:6 there understands this as a "make-up" bracha (tashlumin) similar to missing Tefilla. He rejects the S.A., (because of safek berachos lehakel) in favor of those who only apply tashlumin under the korbanos category, like tefila, whereas one bracha of hoda'a would suffice for both "bathroom breaks".
This is somewhat inconsistent with the M.B.'s own remark in 7:1 where even though there is no specific time limit to say Asher Yatzar (Pri Megadim), you lose the bracha once you need to go to the bathroom again (Shaarei Teshuva/achronim).
I recall somewhere (I can't remember where) that once you need to go to the bathroom, you cannot make the bracha lechatchila because you need to go to the bathroom. This catch 22 would seem to require you to rely on your Asher Yatzar following the 2nd bathroom and would make the M.B. in 7:1 consistent with M.B 7:6.
I believe it's until the next time you need to use the restroom.
Yechawe Daat 4:5, Yabia Omer 8:22 Rav Ovdaia writes you have 72 minutes, however the Hida, the Ben Ish right and, the Or Lesion write only 30 minutes (see Kaf HaHaim 7:7).
The reason Hacham Ovadia holds 72 minutes is because he quotes a Ritva that holds like this and claims that even the Hida and the Ben Ish would go back on their Pesak if they saw this Ritva.