@shallow graveAny post I write depends on my motivation to write. Sometimes I hyper-fixate and bang it out in mere minutes, but then I have moments where I keep distracting myself (*cough* video games and youtube *cough*) and it takes me hours if not days to post any material. Typically, though, it takes me an hour on average/most to write a post for the roleplays I participate in.
Lengthy posts can be established by being descriptive with your writing. It can be information in regards to the scenery, or perhaps even your character's thoughts about the current scene. If you do this, you in turn pad out your writing without the need to step on someone else's toes. It causes your post to appear as if you're doing more when you're not doing much at all.
Just be careful not to delve into purple prose territory, however.
As for your other question, I fully expect everyone to read each other's posts regardless if certain parts of it are applicable or not. Your character doesn't have to
react to everything, but you still have to
pay attention to everything. Roleplay is a collaborative exercise, you're not here to jerk yourself off because you want to solo-write a novel instead like some people I know on this site. The point of roleplay is to build off each other to make something interesting; not become the new GRRM.