Going strictly off of the limited info you gave, sounds like the smaller female has a chance at being gravid while the larger ones chances are quite slim. In the instances where I have clearly seen ovulation, the male seems to lose interest withing days, long before the post ovulation shed which is sometime around three weeks later (give or take).
Has your smaller female shown signs of being gravid?
Unless the larger one was right at the ready to breed point when you introduced the male, would not have happened that quick. I believe it could happen though. I had a female BRB out on breeding loan and the male was only with her for one night, full on copulation and wham, bam, thank you ma'am he was done with her, she took and delivered a litter of 17 babies. Not bad for a first time mom.
Oh yeah, with typical POS at 3 weeks, parturition at POS + 105 days, that's 18 weeks. so before summer if at all. Again, based on total lack of interest by the male.
Not an expert by any means, maybe others will have better info??
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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

