You can post in as many threads as you want simultaneously, as long as the threads are not occuring at the same time in-game. So, for example, your charrie can't be having a shower at 7:45pm on Thursday in one thread, then playing basketball at 7:45 on the same Thursday in another thread.

If time and day are not specified in the thread, then it is up to you to decide and put in your post that it is a different time from whichever thread or threads you already have up and posted in.