1x Rep = 60 seconds total ..... 
20 seconds of calve raises
10 second hold at the top (on tippy toes)
20 seconds of calve raises
10 second hold at the top (on tippy toes)

So, 3x Reps = 3 Minutes Total .... 
20 seconds of calve raises
10 second hold at the top (on tippy toes)
20 seconds of calve raises
10 second hold at the top (on tippy toes)
20 seconds of calve raises
10 second hold at the top (on tippy toes)
20 seconds of calve raises
10 second hold at the top (on tippy toes)
20 seconds of calve raises
10 second hold at the top (on tippy toes)
20 seconds of calve raises
10 second hold at the top (on tippy toes)

Etc ....