IN (as a complete line with possible junk words) open always open Mon To Sun : 24 hours Mo-Su: 00:00-24:00 OUT: 24/7
I'm not completely convinced that "open" should be transformed into 24/7. I think some people write "open" to mean "it's sometimes open" (i.e. as opposed to "closed") but they don't have the information on when exactly it's open. Of course it's OK to interpret it as 24/7 when showing when the place is open (for lack of better information), but I'm not sure that actually transforming it the source information to 24/7 is a good idea. For the other three it makes sense indeed.
Technically, "open" as "sometimes open" disagrees with the documented meaning. This could be brought up in a wider forum, to get a range of opinions. Tools parsing "open" value will miss such intricacy and will evaluate it to 24/7, however since "open" is already a valid OH value, leaving it unchanged seems like a reasonable approach.