Convert String to Real Date Time Value in Google Sheets

This will fix it for you:

=text(regexreplace("timestamp","^\w{3},",""),"MM/DD/YYYY")

you could also transform to remove the additional time parameter at the end with this:

=text(regexreplace(regexreplace("timestamp","^\w{3}, ",""), ", \d+:\d+\w+",""),"MM/DD/YYYY")

OR if your data consistently is formatted the way you did in your examples (with the commas present) you can simply do this:

=TEXT(REGEXEXTRACT(C10,",(.*),"),"MM/DD/YYYY")

Since this is more a regular expression logic update, I can contribute:

Try:

'^(mimz|mi[n-z]|m[j-z]|[n-r]|sa[a-m]|san[a-d]).*'

Just keep in mind that the range above needs to differ by the first character. If not, then pull the common characters out. For mimz-mitz:

'^mi(mz|[n-s]|t[a-z]).*'

Not saying there isn't an easier way -- this just helps you update this particular way in the future.