There's also the position of the Earth relative to the sun. I assume that's what the astrologers are pretending to account for, since that's what knowing the date tells them.
Yes, the Sun is pretty darn far away too (93 million miles on average). Let's say the date and time used as an input to their astrology algorithm is off by 12 hours, since this would place them on the other side of the Earth for a given day (7917.5 miles away). This represents only a 0.0085% and 0.0020% error in the distance to the Sun and Jupiter, respectively.
What I'm saying is that calling out errors in DST and time zone is not a very scientific debunk of your friend's interest. I'm not a practitioner of astrology myself. However, I like to keep an open mind on nearly any topic, especially on something as harmless as astrology. I hope your friend didn't take the criticism too hard. It's always a bummer to find an interest or hobby that brings you joy, just to have it torn down by someone who you respect.
Also, just this week I saw an article posted on Lemmy about how studies show a full moon negatively impacts sleep quality, even if you are in a room with no windows and can't be influenced by the additional light. There's clearly still things about gravitational bodies we don't yet understand.
I don't see it as harmless at all. It promotes belief in other pseudoscience, like various kinds of alternative medicine. People literally die from using fake medicine instead of real medicine. It's also a scam, and I hate scams.
You're also missing that the astrology book itself is where the idea came from that the exact time of a person's birth is important to making accurate predictions. If anything, your commentary about the time being irrelevant is an argument not just against astrology in general, but against that author in particular.
I'm not following on how it promotes belief in "other pseudoscience." I'm also not sure who decides what is pseudoscience and what is not. I just tried to demonstrate on why the physiological influence of distance gravitational objects is still a great mystery to humanity. I fear that the assignment of these binary labels, and shutting down any discussion of alternative possibilities, is rooted in authoritarianism and is more of a threat than any possible scam.
Regarding exact dates and times, of course, the most accurate input is always preferred. The neat thing about astronomy is that we can actually calculate the approximate location of gravitational bodies at times, in both the past and the future. If you are confident that you know the time of an event to a millisecond, by all means, please use this data with all the accuracy available to you. However, even if you are wrong by a significant amount, this error does not scale linearly with the overarching calculations. I tried demonstrating this by using the absolute maximum error of our position relative to the Earth's rotation. In sum, this error was insignificant.
I'm sorry if I made any assumptions. I thought that since you used this evidence to make a point to your own friends, that you thought these errors were significant. However, I guess it could just be the "Cult of Science" mentality @agamemnonymous was describing.