I've been exercised about the pros and cons of the Monastic Office compared to the Roman - and of course, the one thing we all want to know about is, Which is longer?
Breviarium monasticum juxta regulam s. patris Benedicti, ad usum Congregationis ss. Vitoni et Hydulphi Ad usum congregationis SS. Vitoni et Hydulphi. Pars Hyemalis-Autumnalis. By Benedictines
(Not having mine own copy of the Breviarium Monasticum, I made use of Google Books for the purposes of making certain comparisons.)
Well, the short answer is, the Psalmody of the Day Hours of the Monastic Breviary is about 4% longer on average, but of course the Monastic Office lacks certain elements of the Roman - it has only two short responsories a day as against five, no Nunc dimittis at Compline, and, at least in the Farnborough Abbey edition, there is no Officium Capituli at the end of Prime. On the other hand, it does have Kyrie and Pater noster at every Hour, which is much to be desiderated. So overall the two are roughly the same length within the limits of this rough measurement.
Short answer to question: The two are each just about as long as the other.
The longer answer is that the devil is in the detail!
For a start, Monastic Lauds is almost twice as long as the Roman, and no wonder: every day it consists of Psalms 66 and 50, then two variable psalms and an Old Testament canticle (on Saturday, the canticle is so long it's broken into two, and only one psalm accompanies it), and then Psalms 148, 149 and 150 sub una Gloria Patri, for a total of seven psalms and a canticle. Prime, on the other hand, is exactly the same length in both rites, despite having quite different psalms allotted to it. Still, of the 289 psalm verses on average in the Monastic Diurnal's psalmody each day, 148 of them - half - are got through at Lauds and Prime, which makes their recitation rather daunting! (I try and say Roman Lauds and Prime before work; I doubt I'd be able to if I used their Benedictine equivalents.)
The Rule of St Benedict wisely provides that Terce, Sext and None be short; they are in fact each only about two-thirds as long as the comparable Roman Hours. What a relief after Lauds...
As for Vespers and Compline, Roman or Monastic, their length is almost the same.
My final reflection: while Traddies do tend to deprecate the psalter reform of Pope St Pius X, he did make it possible to get through all 150 psalms in the week* - which remains no mean feat even with the '62 Breviary, I can assure anyone: you need to devote an hour a day at least to it! - and did so by using each psalm only once, rather than repeating psalms on different days (as is done at Lauds, the Little Hours and Compline in the Monastic Breviary, and as was done even more in the pre-1912 Roman Breviary, which included such fatiguing joys as praying the whole of Psalm 118 every day). As a result, even if one only prays the Day Hours of the Roman Breviary, one is exposed to 115 of the psalms, over three-quarters of the total - whereas, because of its repetitions, the Benedictine Diurnal only includes 72 psalms, just less than half of the Psalter.
*Recall what the Holy Patriarch St Benedict said in his Rule (chapter xviii):
We especially impress this, that, if this distribution of the psalms should perchance displease anyone, he arrange them if he thinketh another better, by all means seeing to it that the whole Psalter of one hundred and fifty psalms be said every week, and that it always start again from the beginning at Matins on Sunday; because those monks show too lax a service in their devotion who in the course of a week chant less than the whole Psalter with its customary canticles; since we read, that our holy forefathers promptly fulfilled in one day what we lukewarm monks should, please God, perform at least in a week.
What then of the Night Office? (Which is called Matins, rather misleadingly, in the Roman, and Vigils in the Monastic terminology: both contain one or more Nocturns.)
It is said that an angel revealed to a desert Father that twelve was the appropriate number of psalms for the Night Office, and this is the number adhered to in the Monastic Nocturnal. Be that as it may, in the Roman the number nine - no doubt in honour of the Nine Choirs of the angelic host - was settled on for feasts long ago, and since 1912 this has been the number of psalm-portions for each night. Note how much longer Monastic Vigils must be: it must get through 78 psalms (some divided in twain) each week, and each Hour begins not just with Psalm 94, but with Psalm 3 beforehand. Most holy, but very lengthy... Whereas the Roman arrangement since 1912 has only had to cover 35 psalms a week, or 5 a night (again, breaking longer ones up into parts, as in the Day Hours as well), plus the prefatory Invitatory (Ps 94).
Again, I find Roman Matins quite long enough, and quail at the very idea of attempting Monastic Vigils.