SHORT BACK CLOSED ROUNDED VOWEL [u]
In unstressed closed syllables, Tiberian Hebrew shureq/qibbuṣ is normally pronounced as a short u-vowel. It is worth noting that this pronunciation generally also applies to the conjunctive vav before במף or shewa.
LONG BACK CLOSED ROUNDED VOWEL [uː]
In stressed and/or open syllables, shureq/qibbuṣ is pronounced as a long vowel [uː].
(in open or stressed syllable)
EXTRA LONG BACK CLOSED ROUNDED VOWEL [uːu]
In a stressed closed syllable, ḥireq is pronounced as an extra long vowel [uːu].
(in stressed closed syllable)
SOURCES AND FURTHER READING
Khan, Geoffrey. 2020. The Tiberian Pronunciation Tradition of Biblical Hebrew. Cambridge: Cambridge and Open Book Publishers. §I.2.