Time is a twisted and distorted thing in RP, even more so in PS. In PnP RP, you have the usual "Fast Forward time", used on everything that isn't particularly interesting (chars sleeping, travelling, etc.). Likewise, you have postponing, resuming and sequencing of parallel timeframes all the time. However, the settings clock moves at the exact same rate as IRL in PnP RPGs (At least I am not aware of any RPG where a RL clock, if brought into the world, would be significantly faster / slower in completing one cycle).
In PS, there is is an additional issue, which has been discussed before CB: time should be so that players can experience both day and night even if they are 1) in different timezones (forbidding the PS clock to run at the same pace as the RL one), and 2) don't have much time to spend in PS, mandating shorter time periods.
That is why the PS ingame clock runs way faster than the RL clock, a fact that I am not happy about (I proposed a RL day to equal about 2 - 3 PS days at most).
The next problem is that of duration of any action.
Taking interaction as measurement, it would mean that ingame time needs to be much slower than RL timen, beacuse typing in / reading takes way longer than saying and hearing the same sentences IRL. Add to this that due to this fact, people leave out a substantial part of fleshing out (i.e., conversations tend to be "to the point" and usually don't have much of the usual introductionary / outroductionary content), and this time becomes even longer.
Taking the duration of actions as measurement: mining, running from Hydlaa to Ojaveda, etc., all take significantly shorter than the corresponding actions do IRL. The reason for this is, obviously, that players want action in one way or another, and thus would get bored if these would take realistic time. Thusly, the ingame clock must run significantly faster than the RL clock.
Thus, the timeframe which the PS ingame clock provides, is actually perfectly meaningless, as it is an average over the mentioned effects, and as such fails to synchronise to any of them: it is too short to truly RP a night (there's only 10 RL minutes of semi-darkness), it's too short to have a conversation that doesn't last for an ingame hour even if it's just a superficial exchange of politeness, while it is way too long in terms of production cycles (with the output of one single miner in one PS day, one doesn't need the huge machines that exist IRL).
Then add the fact that there cannot be a universal timeframe that applies to every character, simply because their ingame time varies so widely, a problem that is not present in PnP RPGs.
Thus, it is impossible to set fixed, universal timeframes, lifespans, aging rates or gestation periods for PS, because they would simply not be applicable to 80% of the characters.
The usual way is to only use approximate times (preferrably not using any numbers at all), and refer to the timeframe that your RP buddies have adopted at that time, which tends to result from average ingame time and frequency, as well as from events that suggest a certain timeframe.
Many (all?) players have come to ignore the PS clock entirely and simply go by the RL clock, making 1 PS year = 1 RL year. However, in case of infrequent players, this relation doesn't work as well. Most time-related things in PS are governed not by time, but by RP.
Thus, as has been suggested, don't aim for a fixed time, use your judgement for when the time is right.
Since you have asked for opinions on gestation periods: I assume a ~9 months timeframe for all races (except the Kran). Likewise, I assume a similar lifespan for them (including Kran), but since I and most others tend to not use explicit time, this doesn't really matter.
BTW, there have been some proposals for Kran reproduction, but IIRC there's nothing official on that.
