I am aware of the gestation periods of Betazeds is 10 months and (obviously) humans, but is the time span ever addressed of Klingon gestation? (Perhaps VOY might have a reference with B'Elana's pregnancy, but I'm looking for purely Klingon)
From Memory Alpha:
Klingon pregnancies normally ran thirty weeks, but with mixed species, gestation times were shorter.
Presumably those are standard Earth weeks.
In the Voyager episode "Lineage", the EMH discusses Torres' pregnancy with her husband;
PARIS: When is the baby due?
EMH: Normally, Klingon pregnancies run thirty weeks, but with mixed species it could be sooner.
Given that the EMH contains "the collective information of 2000 medical references", I think we can assume he's reasonably expert on the subject.