Tobitronics
You'd have to contact your FTO and BA for exact dates. In my honest opinion though I don't think they'll tell you anymore than what's already on the website at this stage.
Most people are waiting patiently and will attend the assessments whenever they are told to with whatever notice and at whatever cost so bear that in mind. Having said that if you do have some pressing/ non-negotiable engagements approaching I can't see it doing any damage getting in touch and seeking further info.