How long should a person wait to get into a serious relationship after divorce?

Depends on how that person feels and believes what a relationship is. There are those who still believe a relationship is forever and if it dies, they grieve the loss as death itself and the time to start another relationship is as long as the grieving process takes. Then there's the Hollywood relationship where the serious relationship is already ongoing before the actual divorce. So it depends on the individual and his/her environment.