So I was wondering if we knew exactly how long it took Herakles to complete his Labors? I think I remember reading twelve years in total (one for each, presumably), but I can't find an actual source for it. Not an ancient one, at least.
First of all forgive me for the suuuuuuuuuper long awaited answer my dear Anon! Forgive me! If you can still see this.
Well actually we do have a mark in Apollodorous's Bibliotheca (and also other sources such as homeric scholia or Tzetzes). He is rather specific haha he says that Heracles accomplished his labors in exactly eight years and one month:
τελεσθέντων δὲ τῶν ἄθλων ἐν μηνὶ καὶ ἔτεσιν ὀκτώ
After he had finished his labours in eight years and one month
That number seems to be symbolic for the eight years (or cycles of 4 years) play a great importance in ancient Greek calendar in for instance celebrations like Pythia being held at 8 years time (or Olympic Games being held every 4 years) but also in myths the redemption or other arcs seem to last that long (Cadmus serving Ares for 8 years as a redemption for killing his dragon offspring)
The punishment for homicide also seems to be banishment for about 8 years and since Heracles was being redeeming the murder of his children with Megara, the 8 years time seem to be a logical time for him to serve Eurystheus.
That period of time is also mentioned as "great year" unless I am mistaken and it was equivalent to eight ordinary years. (according to Frazer)
Now the one month extra seems to puzzle Frazer a bit so he does try to see it as an addition to the lunar or solar calendar so the banishment being mundane for 8 years and the month extra have something to do with the alignment of celestial phenomena but can't explain much (if you ask me that one month extra could easily be Heracles being led astray here and there during his labors but hey who am I to know? Hahahaha)
Anyways the point being that Heracles most likely took 8 years to complete his labors and not 12.
I hope this helps! ^_^