Animation length / duration / number of frame


I am trying to create a character for an independent game I’m working on. So far, the mesh, bones and rigging are done. I even have a few animations done and I can play them “InGame”.

I am fairly new to Blender. This is what I know so you can get an idea of where I stand.
Once your characters mesh/bone and rigging is done, you can make animation clips. You can create a clip from the “Dopesheet”. Then from the pose mode (in 3D view), you move your character around and then set a keyframe at certain interval. I think you can use the Graph Editor to decide how bones move between each keyframe, but I have yet to use this feature. The timeline shows where your animation starts and ends, as well as where you inserted keyframes.

So here is my problem:
Is there a way to specify an “animation length” in frame for every clip you do? It seems you can only specify one “start frame” and one “end frame” in the timeline. I find this put a really big constraint on making animation clips, as every clip you do (walk, run, jump, roll, idle, etc.) must have the same length in frames. It is possible to change the speed at witch the animation plays in the game, but I feel this is more of a patch than a real solution. I stumbled upon the NLA editor, but I am really not sure if this is what I am looking for and even how to use it.

I searched the forum before posting this and I found some questions that might relate to my problem but never exactly what I was looking for. If someone could answer my question, or help me put the pieces together, i would greatly appreciate it.

Here is what i found as I searched the forum:
good description of every view for animation: /t/character-walk-cycle/504398/1

similar question, but i don’t understand the answer: /t/changing-frame-length-of-action-to-match-first-and-last-keyframe/493663/1

again, similar problem, but they only mention the NLA editor: /t/start-and-end-frame-for-animations/528478/1

Again, it might just be because of my incomplete understanding of blender, but exactly what is exported when you export to .FBX? It seems to me that every clip created in the “Dopesheet” become a clip and I thought that since you add the clips in the “Dopesheet”, that would be where you specify the length of every clip, but I’ve been unable to find anything so far.

Thanks a lot, I hope I was clear enough. English is not my native language, so if you have a hard time understanding what I meant, I can try to rephrase it.