In Holy Communion and the Worship of the Eucharist Outside of Mass it has in n. 91: “The ordinary minister for exposition of the eucharist is a priest or deacon. At the end of the period of adoration, before the reposition, he blesses the people with the sacrament.”
Then it describes how other people may “expose and later repose the holy eucharist for the adoration of the faithful” for situations “in the absence of a priest or deacon”. The description ends with: “It is now lawful, however, for them to give the blessing with the sacrament.”
So, in general, if a priest or deacon is reposing the blessed sacrament without the blessing he doing things incorrectly. He is doing things the way a lay person would do them.
But here is an exception to that, where a priest or deacon does repose the blessed sacrament without a blessing, as described in Holy Communion and the Worship of the Eucharist Outside of Mass n. 88, under the heading “Lengthy Exposition”:
“88. If a period of uninterrupted exposition is not possible, because of too few worshipers, the blessed sacrament may be replaced in the tabernacle during periods which have been scheduled and announced beforehand. This reposition may not take place more often than twice during the day, for example, about noon and at night.
The following form of simple reposition may be observed: the priest or deacon, vested in an alb, or a surplice over a cassock, and a stole, replaces the blessed sacrament in the tabernacle after a brief period of adoration and a prayer said with those present.”
In n. 89 it has “Exposition which is held exclusively for the giving of benediction is prohibited.” So, it seems to me, that having a five minute ceremony where there is exposition, prayer, blessing and reposition would not be complying with this. But, it seems to me, it would be no better to have a five minute ceremony without the blessing, of exposition and reposition.
[Excerpts from the English translation of Holy Communion and the Worship of the Eucharist Outside of Mass © 1974, International Commission on English in the Liturgy Corporation. All rights reserved.]