Mixed dates that need to all be the same format

welcome to the forum, aigo. Excel recognises dates as integers & time as decimals. to verify, type in 1jan2013 in C1. and 12 pm in D1. Format both cells to General. you will see that A1 is 41275 (meaning 41,275th day from 1 Jan 1900) & B1 is 0.5 (1/2 a day).

so if you select the range & press CTRL + SHIFT + ~
you should see only some of them become numbers if they are real dates. Undo it to revert to normal. if they are all numbers, you can simply right-click & format cells into whichever format you desire

but they are not. if your dates are consistently wrong (like all in DMY or MDY, etc), select the range again (A11:A272). go to Data -> Text to Column -> Delimited -> Next -> Next -> Date: MDY -> Finish. i select MDY because the dates seem to be in MDY. to know, look at those dates with bigger than 12. months cannot possibly be bigger than 12, so it seems like the day is in the middle.

do the same for column B. now, you can format both column's date format