Lots more people would have the same birthdays.

I had the discussion the other day of how civilization would be different if humans followed the 'have loads of babies at once and see which ones survive' style of reproduction.

"Oh hi Sarah! How're the kids?"

"Oh, little Jeremy wasn't eating as much as the others so I threw him outside onto the road."

MTV's Spring Break would be a lot crazier.

Maybe my wife would actually have sex with me?

Does it happen en masse or does each woman have their own heat season? Say, does everyone go crazy during the same 2-3 weeks or does it vary per person like it happens with periods?

In the masse heat I think there would be some obvious differences in stuff like festivities and each culture would adapt to these seasons. There would be a need to gather and store resources before the rut, and also to be prepared for the inevitable birthing en masse to come. We would probably have public holidays for the mating seasons and festivities for birthing season. In contemporary times, hospitals would need to do some heavy work planning and preparing maternity ward space to accommodate the seasonal influx. That's just what pops to mind.

Not too sure about the differences in the second case though. One option is, women would be allowed to retreat from society and become hermits during heat if they want to avoid pregnancy and this would be totally normal. Or, some cultures would lock them to prevent them getting pregnant. Coming to think of it, I think having women randomly in some kind of irresistible heat like this would be very disruptive and impossible to prepare for so I don't see much happening in the way of gender equality and women's rights sadly. I'm inclined to think the re would be a lot of gender based extreme segregation.

I'll point out that many creatures that have seasonal mating still mate for life.

O.O

Do you want to read this part again slowly, out loud, then consider this from a female point of view.

non pregnant women produce pheromone that men can't resist and start calling every boy around to breed with them.

Women have enough problems with unwanted male interaction, not to mention so many lies about women's anatomy. This makes it so much worse.

I imagine it would look a lot like how Zoidberg’s home world is depicted on Futurama

first two things come to mind:

water-cooler conversations at work would be different. telecommuting may be an important option during the season.

My shiny seashell collection may be in jeopardy. the ladies love seashells 🐚.

From what I have heard/been told the "ignoring partner and sex 1-2 times a year" is a lot of marriages, so maybe your scenario wouldn't change much

Reminds me of how the Vulkans have it in Star Trek. I'm no expert but there was an episode where Spock went into his horny craze :)

Post nut clarity for most of the year sounds peaceful, but I'm guessing people in heat would think with their genitals and wouldn't care about STDs or pregnancy.

Everyone wound have some STD and birth control would be a side note. Human reproduction would work like clockwork and without neutering world would have exploded long time ago.

We sort of do