I am looking for a 30 - 40min cyclocross race sim workout.
For pure race simulation you’re looking at sessions which target bouts at VO2 Max and/or Anaerobic power levels, examples - over:unders/ 120%:75% time ranges can be progressed from 20:40/ 30:30/ 40:20 etc etc. Repeated sprint power can also be of focus as can undulating efforts such as 10 minutes of 2 mins @ 110% 2 mins @ 85% repeated.
Never discount the benefits of a cross group ride either, sandy circuits/ grass hills all make perfect areas for you to race your mates in a competitive but fun environment for you to get the most out of yourself!