I'd say from my own experience that entering the refractory period, after an ejaculatory orgasm, is partly voluntary, and you have some control over it.
If I keep my erection going with sexy thoughts about the lady and/or light stimulation, then I don't lose my desire to do the lady again. And I can do it too for the second time, after my ejaculatory orgasm.
But if I simply stop and don't try to maintain my mood to do the lady good for the second time, then I lose my erection and my sexual desire. And once I enter this refractory period, then it might last for some time.
So, the trick is not to enter the refractory period in the first place, rather than try to come out of it.
I think entering the refractory period is partly under voluntary control. Because there is some evidence that the refractory period is mediated by the Prolactin hormone, which is secreted by the Pituitary gland in the brain. This Pituitary gland is connected with the brain. And that's why thinking sexy thoughts about the lady and/or getting some stimulation to keep your erection going might prevent the secretion of the Prolactin hormone and your entrance into the refractory period.
https://www.medicalnewstoday.com/articles/refractory-period#malesBiologically speaking, it makes sense to have some voluntary control over whether you enter the refractory period or not. Because when you are with two ladies or more, and you've already done one of the ladies, then it would be advantageous to keep going and do the other ladies too. Or else you will lose the opportunity and never get to do the other ladies.
In terms of evolution, it makes sense for guys to have this kind of ability to adjust to the situation and be able to take advantage of it. And if you understand how it works and why, then you can have conscious and voluntary control over it by thinking and behaving in the right way, after your first ejaculatory orgasm.