I have a formula duration field that calculates elapsed time (hh:mm) between a start time and a finish time. If the elapsed time is a negative or greater than 8 hours, I want to highlight the text as red.

My field [Duration: Engaged to Recovered] is calculated from the following fields

ToTimestamp([Date Recovered],[Time Recovered])-ToTimestamp([Date ESG Engaged],[Time ESG Engaged])

If for some reason my users enter a recovery time prior to the engagement time resulting in a negative (i.e., -46:15) or recovery takes significantly longer than the norm (i.e. 20:18), I want to highlight this with a red font.

All the formula's I've tried give errors that I can't use a "duration" < "number" syntax. I've tried creating a new formula text field, formula number field ... I'm stuck.