Now that you mention it and I think of it: One could write the timestamp to a session variable when the user visits the landing page and check the seconds between that timestamp and the time the claim is being "processed". There's no way to cheat on that.
I actually
suggested that previously with a small example of code to show what I'm talking about. Is this similar to what you mean?
exactly isn't antibot links js? I've not used it but I have my own antibot links which are JS as well as a maths question also JS and yeah they skip right past them. So couldn't you return a checkbox in send() function which must be clicked first to send? Not JS.
Any HTML checkbox could also be automatically selected by just adding 'selected' into the tag. Anything that the user can see (Javascript, HTML etc) and is in plain text is very easy to manipulate if you make it obvious; you shouldn't rely on things like that to stop bots. You should use PHP (or another server side language) verification which the user cannot see or edit to stop bots.
Also, to follow on from what BitBustah said:
A scammer could easily read that "anticheckbox" variable and send it by default. It would be better if you used sessions and create a variable name for the input variable. Then the code would always be different.
You should also add several checkboxes into your page with other variable names, else they could just check the first checkbox they see and get it right.