I'm not really sure what your question is. We don't leave out words when we speak. Could you clarify?

我所知的不是省略“is”不读，而是弱读，可以直接读成/z/

In this sentence, a weak form of IS is used. The length of the sound of IS is reduced. So it's hard for a learn to hear the sound.

Definitely no. When you say "his time limited" in (sloppy) spoken English with a questioning tone, you are actually asking "(is) the time limited?" Like "(are) you good?", "(do) you like it?", etc.