Most schools say that prior to going on your first solo that you have passed the Airlaw exam. The rest can be taken in any order - but probably best to take them as you are introduced to subject matter whilst flying.. i.e. don't start by studying for Nav exam until you start the practical side - maybe a wee bit before it anyway..
Correct me if I am wrong here folks but timescales are along the following..
After passing the first exam the clock starts ticking. You have 18 months before this exam expires. After passing all of the written exams you have 24 months to complete your Skills Test.
Details will be listed in LASORS on the CAA website.
Hope this clears the fog slightly!!!