First on the mighty Timaeus’ chronological excellence, your simple faith was not shared by those who actually read him;
Dionysius of Halikarnassos 'Roman Antiquities' Book I
74 As to the last settlement or founding of the city, or whatever we ought to call it, Timaeus of Sicily,196 following what principle I do not know, places it at the same time as the founding of Carthage, that is, in the thirty-eighth year before the first Olympiad;197 Lucius Cincius, a member of the senate, places it about the fourth year of the twelfth Olympiad,198 and Quintus Fabius in the first year of the eighth Olympiad.199 2 Porcius Cato does not give the time according to Greek reckoning, but being as careful as any writer in gathering the date of ancient history, he places its founding four hundred and thirty-two years after the Trojan war; and this time, being compared with the Chronicles of Eratosthenes,200 corresponds to the first year of the seventh Olympiad.201 That the canons of Eratosthenes are sound I have shown in another treatise,202 where I have also shown how the Roman chronology is to be synchronized with that of the Greeks.
Polybios 12
4a Who could continue to pardon such faults, especially when committed by Timaeus who is so fond of cavilling at similar blemishes in others? 2 For instance, he accuses Theopompus of stating that Dionysius was conveyed from Sicily to Corinth in a merchant ship, whereas he really travelled in a warship, 3 and again he falsely accuses Ephorus of making a blunder because he tells us that the elder Dionysius began to reign at the age of twenty-three, reigned for forty-two years, and died at the age of sixty-three. 4 For surely no one could say that the mistake here was the author's, but it is obviously the scribe's. 5 Either Ephorus must have surpassed Coroebus and MargitesJJJ in stupidity if he could not reckon that forty-two added to twenty-three make sixty-five, 6 or as nobody would believe this of Ephorus, the mistake is evidently due to the scribe. No one, however, could approve of Timaeus' love of cavilling and fault-finding.
This is especially interesting since it concerns the length of a reign and a life which far from checking against other records and adducing these he seems merely to have relied on the seemingly faulty mathematics.
All the same Plutarch probably took his information from Hegesias not Timaeus,
5 Be that as it may, Alexander was born early in the month Hecatombaeon,5 the Macedonian name for which is Loüs, on the sixth day of the month, and on this day the temple of Ephesian Artemis was burnt. 6 It was apropos of this that Hegesias the Magnesian made an utterance frigid enough to have extinguished that great conflagration. He said, namely, it was no wonder that the temple of Artemis was burned down, since the goddess was busy bringing Alexander into the world. 7 But all the Magi who were then at Ephesus, looking upon the temple's disaster as a sign of further disaster, ran about beating their faces and crying aloud that woe and great calamity for Asia had that day been born. 8 To Philip, however, who had just taken Potidaea, there came three messages at the same time: the first that Parmenio had conquered the Illyrians in a great battle, the second that his race-horse had won a victory at the Olympic games, while a third announced the birth of Alexander. 9 These things delighted him, of course, and the seers raised his hopes still higher by declaring that the son whose birth coincided with three victories would be always victorious.
Just to be complete Cicero does say in De Natura Deum (On The Nature of the Gods)
There is a remark of Timæus which, like many of his, shows ingenuity; after saying in his history that the temple of the Ephesian Diana had been burnt down on the same night that Alexander was born, he added that that was by no means to be wondered at, since Diana wishing to be present at the delivery of Olympias had been absent from her home.
The simplest explanation would be that Cicero has erred, as it is hard to imagine anyone, especially a writer noted for the ‘frigidity’ of his prose (pseudo-Longinus), choosing to repeat such a lame statement, the Tullian Chickpea’s judgement notwithstanding.
Arrian says
εἶναι δὲ τότε ἀμφὶ τὰ εἴκοσιν ἔτη Ἀλέξανδρον
At that time Alexander was about twenty years old.
No ‘around about’ either one but not both; nor does it follow that Arrian took this opening summary from Aristoboulos, more probably it was his own work and the ‘amphi’ about, is due to him possibly not being sure that Alexander had had his twentieth birthday by the time he ascended the throne; I have no doubt that a contemporary flatterer, like Aristoboulos, would have known but it would seem he made no mention of it; his History may have started with the expedition into Asia and not the beginning of the reign.
Good try at confusing Aristoboulos’ contempory statement with Arrian’s later transcription information has to be judged on the source (if possible) not the transmitter (unless there is reason to suspect a sloppy worker – such as Diodoros).
The explicit date for Alexander's birth in Plutarch is clearly preferable unless you are one of the true believers in the infallibility of Arrian (notwithstanding the fact that he is the latest of the main 5 surviving sources on Alexander and was further from Alexander than we are from Shakespeare).
As mentioned it is in Aristoboulos I place my trust, rather than Arrian. Justin is much later than Arrian but the point is moot since these secondary sources must be ranked by the quality of the primary sources they used. Arrian used Ptolemy and Aristoboulos two men close to Alexander who were on the expedition. Curtius certainly used Ptolemy, but, like the earlier Diodoros seems to have preferred the account of the later Kleitarchos who had not been present during events. Plutarch, whom it must be remembered is not writing history, is an amalgam of many sources and probably cod-sources too, which is the real reason he does not notice the anomaly between Aristoboulos’ dates and the birthdate he has given, he is not correlating and evaluating many sources, simply cherry-picking illuminating and interesting stories. Justin, of course goes back to Trogus a contemporary of Diodoros who may have based his work largely on Kleitarchos or a derivative. So due to his use of true primary sources Arrian’s account preserves the earliest strands of the major five sources.
When you think about, it free-choice is the only possible option.
Apparently in ancient times there could be two growing seasons, but the most abundant crops were those which were planted in the fall and harvested in the spring. There's this from 
