I'm sure someone has thought about this before, but instead of having the client do work for a certain amount of time, could you just disable submit, set a java

I'm sure someone has thought about this before, but instead of having the client do work for a certain amount of time, could you just disable submit, set a javascript timeout for some set amount of time, then enable submit after that? Why does the client need to be processing during the waiting time? Would spambots wait around for the submit button to work?