The rite of anointment and imposition of hands can be dated with certainty to the sixth century. In the fifth and sixth centuries the Goths of Gaul and Hispania belonged to the Homoian church (by Nicene Christians denounced as "Arian"). The pastoral need to have a rite of reconciliation for the former "Arians" existed thus only as long as there was the Homoian church. King Reccared converted to the Nicene faith and he also gathered the general council in Toledo in 589 (Third Council of Toledo) which proclaimed the conversion of the whole kingdom. The Homoian church lost its official support and many members and in consequence soon (although probably not immediately) it ceased to exist. It is possible that the rite was composed in the form preserved in the Liber ordinum somewhere around the times of this general conversion as it generated the necessity to reconcile many people who followed the decisions of the Third Toledo.
It is also interesting that the rite contains a special prayer which should be proclaimed in the case of reconciliation of someone who being a Catholic received baptism in the Homoian church. The Homoians in the successor kingdoms practiced a repetition of baptism in the case of "heretics" baptized outside the Homoian church (so also in the case of the Nicenes converting to Homoianism). In 580, the council fo the Homoian bishops gathered in Toledo by Reccared's father, Leovigild, decided to stop practicing the repetition of baptism in the case of the converting Nicenes (we know about this event from John of Biclar, Chronicle c. 57). But it does not mean that the prayer must be earlier than 580. We do not know whether the decisions of the Homoian synod were immediately accepted by all Homoian clerics. Also there might have been people who received the Homoian baptism before 580 but decided to reconcile with the Nicene church after that date, especially in the period following the general conversion of the kingdom.