【實用工具app】KeepTiming|最夯免費app-gigacircle

KeepTiming is the perfect application for exercise, parking meters, cooking and other activity where you need to keep track of time while using your iPhone or iPod Touch to do other things.

But you say "there is already a timer installed". Yes, but that timer will not keep timing while you switch to other applications and allows you no way to pause the timing.