@Ray and Dan, thank you very much for your suggestions. I will give it a try next weekend and report back.
@Dan, your solution should definitely work. This would make scheduling a bit more complicated so I’ll try to incorporate Ray’s suggestions. As from a UI point of view everything is already there apart from the restrictions for negative values it would be nice if theses changes could find their way into the “official” source code. I do believe that some people have similar issues with a “weak” well.