Oh yeah, well I’m ugly too! And besides, that wasn’t a question.

Many siddurim are based on older works. For example, my copy of the Shilo Siddur (a siddur commonly used in America) states that asking for rain commences on December 4. This would be correct for the 19th century. Well, almost correct, since no mention is made of years that fall before a civil leap year, which would begin Dec 5. However, in the 20th century, the correct date would be the 5th of December, and the 6th of December in years that fall before a leap year. This is because the date of asking for rain is calculated according to Rav Shmuel’s tekufot, which correspond to the Julian calendar. This means that the dates slide forward as the years progress. In the 22nd century, the correct dates for asking for rain in the diaspora will the 6th and 7th of December.

Off by a few minutes compared to what? Perhaps this is due to different shitot. Perhaps because of slightly different location coordinates. Not to mention that I have yet to find two sunrise/sunset algorithms that consistently result in the same times. I also have yet to see two clocks/watches that display the same time. My opinion (for what it’s worth) is that the times (from Kaluach or any other source) are of limited use, since I doubt that anyone really has access to the correct time. Care should be taken to always add or subtract a few minutes from the time in question to be on the safe side.

[important note]: It is a minhag in Israel to use the tables of halachic times as compiled by Rav Tucazinski z”l. These tables were derived by sightings of the sun (as opposed to the calculated times in Kaluach and other programs) and are accurate only for Jerusalem and Bnei Brak. Using these tables with adjustments for other cities in Israel is wrong, since the times in these tables are sighted times, not calculated times. These tables are only applicable for Jerusalem and Bnei Brak. For that matter, these tables will eventually shift out of accuracy as the years go by, since the sunrise/sunset times are based on the solar calendar, and the times shift slightly as the years/centuries progress.