If things are straightforward a divorce takes between 4 and 6 months. A lot depends on if your partner responds quickly when they receive the divorce petition. The divorce may also be delayed due to the separation of matrimonial assets, as it is best to resolve these matters fully before you apply for the decree absolute which marks the end of the marriage. The divorce could also be delayed by problems which concern the arrangements for children.
In general, the more you and your partner can agree on, the quicker the divorce process will be.