Orin is still reasonable calm, but I've looked back and it was day 14 that he lost the plot last time, so that would make us think that the eggs were maturing on that day of her last season too. When they are maturing they soften and the sperm finds it easier to fertilize them, though sperm from a health young male can live for up to a week, mating is more successful if the mature eggs are already laying in wait ... The boys were still frantic on day 16 last time, I think they get more desperate as the unfertilized eggs mature, but by day 17 things were starting to settle.
If I had to guess I'd say Siska ovulated yesterday evening, there was a difference in Orin between 5 pm when he went past her to eat his meal, to 10pm when he rejected his carrot and I had to pull him away from her crate (And Orin LOVES carrots!) We always used to say the ideal time for mating was 48 hrs after ovulation, well Sunday morning may be a tad early - but it takes 6 hrs for the sperm to travel to the eggs - we won't be far out! (I hope)
Vet Google says " Following ovulation it takes the eggs 2 days to mature and be ready to be fertilized. Ovulation of multiple follicles may occur over a 12 – 36 hour period. Once mature, the eggs are capable of being fertilized for 2 days. Therefore, the fertile period begins 2 days after ovulation and lasts for the next 3 – 4 days" (Ovulation in GSD bitches is known to be about 17)