You didn’t account for turns. Multiply your 25 times by 4, subtract two seconds for the block start, then add 3 seconds for 3 turns. 11.75 X 4 = 47, add 1 second (-2+3), 48.0 is the predicted 100 time.
Also, at over 18 seconds of rest per 25, you may need to see more like 20 reps to be confident that you’re athletes can hold that pace together for 100 straight.
BTW, the predicted time should be good now, not at the end of the season. What are these guys currently doing in the 100 at meets?