Right, been paper trolling
Spermatogenesis (as a general rule) starts when the temperatures drop at the end of summer and the males will enter Hibernation fully loaded in prep for Spring.
The fact that there have many reports of mating activity observed by multiple species in Autumn (as well as year round) suggest that:
1) Spring mating is the optimum/norm
2) Males/females can be perfectly ready to mate pre-hibernation.
3) Indiviual females may indeed be able to double-clutch where conditions are right .... or .... Females with low fat stores and unable to breed after cooling may still be able to attract males during a successful feeding season later in the year.
In a lot of species you'll see a range in a season (say June-September as an example) in which babies may be born. This could suggest sperm storage and female selected fertilisation times but later matings can not be ruled out.
There are a lot of factors to consider in the wild - food availability/seasonal differences from year to year/etc.
But I would say that it's perfectly possible for breeding to occur at any time of the year (albeit with varying degrees of success).