Well, first off, you can use the PropertyAccess service as a much easier way to get at your dynamically computed property.
What is setting and changing the id? Is TsWhour a component?
Basically, at form submission time, Tapestry will need to retrace its steps to each component and each change of that id property. The Loop component, inside a Form, knows how to do this (though you can configure it to optimize things a bit).
You haven't provided nearly enough context.
Finally, perhaps there's an issue with your data modelling if you have a "gazillion" virtually identical fields. Maybe what you need looks more like a Map than an Object. Maybe you need a simple way to extract data from your entity type (I'm assuming you are using Hibernate or JPA) into an intermediate type that is easier to work with in the UI layer.