For genealogy in general, and Ancestry.com in particular, I prefer date month year: 12 Jan 2020 vs. Jan 12, 2020, but either of these is clear and works well. Be sure to include the spaces - they are necessary for Ancestry. I avoid writing dates as 12/1/2020 because that date is ambiguous and can be interpreted as either 1 Dec 2020 (American) or 12 Jan 2020 (European).
All Refamily Articles & Links for Tag "Entering Dates"
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library_books How Should I Format Dates on Ancestry.com?