Note: I edited your post to fix the code formatting. In future please try and format your code samples so they're easier to read.
It's hard to tell exactly how to fix your problem without knowing your tree structure, but I suspect it's due to having the node path wrong. The path you use in
get_node() is relative to the current node.
get_node("Cronómetro") only works if "Cronómetro" is the child of the current node. If it's a sibling, for example, it would be "../Cronómetro". See this tutorial for more info: https://docs.godotengine.org/en/latest/getting_started/step_by_step/scripting.html
Next, it's not clear what you want to do with the wait time. You can access a node's property directly by its name. For example:
would print the property. A list of a particular node type's properties, or "member variables" can be found in the docs. See Timer, for example.