Schema.org says this,
The opening hours for a business. Opening hours can be specified as a weekly time range, starting with days, then times per day. Multiple days can be listed with commas ',' separating each day. Day or time ranges are specified using a hyphen '-'. Days are specified using the following two-letter combinations: Mo, Tu, We, Th, Fr, Sa, Su. Times are specified using 24:00 time. For example, 3pm is specified as 15:00. Here is an example:
<time itemprop="openingHours" datetime="Tu,Th 16:00-20:00">Tuesdays and Thursdays 4-8pm. If a business is open 7 days a week, then it can be specified as
<time itemprop="openingHours" datetime="Mo-Su">Monday through Sunday, all day
However, when I use that time format I get this on the W3C's validator,
Error Line 1, Column 2898: Bad value Mo-Fr 09:00-17:00 for attribute datetime on element time: The literal did not satisfy the time-datetime format.
…ingHours" datetime="Mo-Fr 09:00-17:00">Mon - Fri; 9 AM - 5 PM (CST)
I've tried with and without padding a 0 on 9:00.