Women may be have the "biological clock" but when it goes off it doesn't just effect women. The biological pathways are complex but if a woman reaches 0 and her alarm goes off she releases powerful pheromones to attract a mate. These pheromones are much more powerful than what is normally created and target childless males exclusively.
Exposure for merely an hour or two has a profound effect on the male, a cascade of hormones and neurotransmitters are released initiating an unparalleled devotion and desire for coupling as well as instigating a surge of testosterone to prepare the male for fatherhood and defense of the household. Its normal for the woman to ensnare multiple men this way cultivating a harem of men as she tries to get pregnant. The men of varying ages and races, producing mega-doses of testosterone, can rapidly gain 10, 20, or even 30lbs of muscle in a month. Within days men she's brought back begin gathering, forgoing hobbies and personal interests to cater to her needs and breed with her.
This sudden community of men continue to go to work but all their free time becomes dedicated to wherever the woman is. free time is spent on enhancing the area she is in and supporting each other by sharing wisdom and skills to ensure that if the other man becomes the father, the man will do well in his role. Home, job, parenting, gardening, cooking, relationship skills and more get passed around like wildfire.
Starting gardens, (re)building decks/patios, privacy fences, remodeling, painting general yardwork, planning, organizing, cleaning, redecorating and countless other things focused on making the space a home are brought out of the men. With a unified goal and sense of shared comradery, its common for men to share the costs and all pitch funds in, in order to keep projects active and moving.
Once impregnated, the baby produces pheromones released through the mother which targets the father. This repels the other men and breaks their bond with the mother but has the opposite effect on the father sparking more nesting behavior and changing him further still. The man already bulked with muscle, will now begin to attain a dad bod over the course of the pregnancy to the extent of possibly graying prematurely, his mere appearance, a tell-tale signal of parenthood.
Huge muscular physiques are seen as a sign of repeatedly failing to impregnate someone but also seen as doing your communal duty and gaining and sharing a wealth of skills and wisdom. It's entirely possible to see what appears to be a burly middle aged man and find out he's a 19 year old, still going to college, but his mom's girlfriend was over and having a tough time with men suddenly giving her so much attention, and things happened.
Once a man is around for the birth of his child and bonds with it, through the biological clock process or not, the male body produces antibodies to remove the augmented effects of the pheromones in the future, rendering them back to their normal everyday state and the man is immune to biological clock effects.
Sex ed classes now warn males to look out for signs that they or their friends are being manipulated by pheromones as they only have an hour or two before they are overwhelmed and going through this would stop your growth, possibly mess up your life by changing all your priorities and making you a father, and likely destroy any current relationships you have.
There are stories of women taking over whole college dorms for a month and a half, grooms being stolen away the night before their wedding, infertile women with ever growing communes of men servants, new father's looking like their dad's brother, interventions to try to free men from these communes, and countless other messy situations that come with being human. Who do we follow?