Generally it's only 12/24 hour time displays that are selectable on Casios. You typically can't change the date format for instance. Sometimes in the Stopwatch function there is a way to see other units e.g. by pressing an extra button or the display automatically changes when one set of units reaches their maximum. However for the SGW-100 the manual states that the Stopwatch only measures up to 59 mins and 59 secs so I think you're stuck with the countdown timer.
https://www.jmt.bg/productfiles/24100_1721.pdf