continue milking the cows for more than a year?

Hi there, since 2 months we have 2 beautifull jersey cows, which we milk. Our idea is to do only seasonal milking (from april untill october). But we might have a problem now.
The cows are still not inseminated, because the sperm didn't arrive on time, because it was hard to find, and so on. Now our next chance would be the beginning of october, which would mean that they would calf around the beginning of july. This is way out of shedule and will be hard to get them into shedule again.
Could it be an option to just continue milking them, without insemination for another year, so we can inseminated them next year in june? I heard from traditional cowkeepers that it is unpossible, but i feel like i need a second opinion on this.
Any ideas?