Is there a particular day of the month that has been shown not to be adequate for buying ETFs?

External question — Personal Finance Stack Exchange Author: D1X Original post: https://money.stackexchange.com/questions/127466 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. This question refers specifically to buying ETFs. When performing dollar-cost-averaging, one typically chooses a day of the month to rebalance. The question is pretty simple: Are there any specific dates and or moments that should be avoided? An answer in this question asserts that one should not buy ETFs at the trading day's opening, for example. Is this also true for particular days?