It seems that there's a 72-minute period after eating in which one must bentch.
Does this also apply for Borei Nefashos and Beracha Me'en Shalosh?
The time limit for all after-blessings (including on bread) is until you become hungry again from what you ate. If one ate a large meal he may have well over 72 minutes before he can no longer bentch. However the issue arises (with bread but even more so with fruit), what if you are still hungry after you finish your food? For instance, if you only have a small fruit or a light snack. At what point does the satiation you got from that food dissipate? This case is where the Halacha says 72 minutes is your best guess for a small amount of bread. For drinks and snacks, no such number is given on the books but I have heard some poskim estimate it to be about 30 minutes. It really depends on the circumstances.
In short, you can say your after blessing on any food so long as you have not yet stopped feeling the satiation of eating that food.
The gemara and poskim write that after eating a big meal one can bentch as long as he is not hungry, this may extend as long as 3,4,5, and so on hours depending on the case. However for a light meal or snack one has 72 minutes. I heard rabbi bess say in the name of rav elyashev that after drinking one has 30 minutes.