The application is relatively straightforward.
The main part is drafting affidavit evidence (ie written statements). These need to cover both the reasons for the original disqualifications in detail and then set out the grounds why the original period of disqualification should be reduced.
That evidence is served on the Secretary of State and it is likely it will then be referred to one of his panel solicitors to deal with. They may respond with their own written evidence or simply attend the hearing before the Judge to make comment.
The length of the hearing will depend on the volume of evidence the Judge has to consider. Normally however, you could expect the hearing to last no more than half to one day. You would need a barrister to attend the hearing to present the case to the Judge and deal with the legal argument.