The Pentecost Octave was preserved in the Anglican 1662 [see the rubric attached to the Preface] and Roman 1962 books. In 1662 and in the pre-1955 Roman Rite the Monday and Tuesday were especially privileged; in the older Roman books they are doubles of the first class with the rest of the week at only semidouble rank, while 1662 kept the traditional lections on Monday and Tuesday but returned to the Sunday readings for the rest of the week. This Octave is suitable if Pentecost is regarded as one of the times for Christian Initiation, since the neonati appropriately wore their 'whites' until Saturday and were catechised. It had survived even the pruning of the calendar by Pius XII in 1955, who curiously evened out the week by making every day a double of the first class ... fattening them up, as somebody once said to me, for the slaughter. Its abolition in the post-Conciliar period [by Rome and then, in mindless imitation, by Anglican revisers] finally 'forgets' the baptismal associations of Pentecost and abandons the message of Acts 2: 38-41. Is there a way in which someone who uses the Liturgia Horarum and has a canonical obligation to say the Divine Office, can, without breach of liturgical law, observe the Pentecost Octave?
One could invoke the General Instruction of LH paragraph 245 and repeat the Pentecost office every day up to Saturday as a Votive Office being celebrated devotionis causa. Indeed, modern Vatican Press Ordines Recitandi say that " where the Monday after Pentecost is kept as festive, Mass can be said as yesterday, or a Votive of the Holy Spirit, with Gloria and Credo pro opportunitate; likewise Vespers or even other parts of the Office if celebrated with the people". But in six days the priest - and the people - might get a bit tired of its inflexibility. Of course, one could simply follow the permission given in Summorum Pontificum and use the old Breviary during this week. Is there any reason why one should not continue to fulfil one's canonical obligation through the saying of the LH office, but substitute some offices from the Breviary for some from LH? The Apostolic Constitution Laudis Canticum (Paul VI, 1970), does envisage that permission might be given by Ordinaries to particular clergy, in their private recitation, "Breviarium Romanum, quod antea in usu erat, sive ex toto sive ex parte retinere [to retain the R Breviary ... in part]". One would argue that this is still the law, except that Summorum Pontificum has rendered the "consensus sui Ordinarii" unnecessary (and has not confined the permission, as Paul VI did, to the elderly or those with grave difficulties). So a priest could say Mattins, Lauds, and Vespers from the old book.
Incidentally, Pope Benedict XVI authoritatively made clear that the old Missal was never lawfully abrogated. I presume this is on the grounds that the Apostolic Constitution Missale Romanum of 1969 contained nothing explicit about the new rite being compulsory and exclusive. But Laudis Canticum does say that, after certain dates, only the reformed office is to be used ( ... tantummodo ... adhibenda erit). Does it follow that the old Breviary, unlike the old Missal, was canonically abrogated until Benedict XVI resurrected it?