No reference shall be had before two months after the filing of the complaint in the office of the Clerk of Court, nor shall a final decree be granted before three months after such filing.
Provided, however, that when the plaintiff seeks a divorce on the grounds of desertion or separation for one year, the hearing may be held and the decree issued after the responsive pleadings have been filed or after the respondent has been adjudged to be in default whichever occurs sooner.