"more" is a comparative word, so it needs to compare to something. More than [something]… More time than we need. More time than we were given. More time than there is left.
“much” is a stand-alone word; it does not compare to something else. If there is much of something this means there is a lot.
'”We have more time to finish this work.” This can be correct if you are saying this to your team, to explain that we have more time than we thought we had, or more time than we had before. (If you have to finish by Friday, and are told you have more time, you know that it is now longer than Friday until the deadline.)
“We have much time to finish this work.” This is a generic statement saying that there is plenty of time.