Time Keeper for Presenter is a perfect solution for speakers to keep track of time and pacing.

Leave it on the desk and keep the timer running.
Timer will automatically start counting up in red after it passes 00:00.
(Completely discreet)

How to use:
Select a timer value from the timer list by tapping and launch timer. Tap on the time text to start timer.

Timer Selection View:
Add Timer: tap the + button
Delete Timer: Swipe at any timer value
Edit Timer: Tap-Hold at any timer value

Timer View:
tap on timer text to start/stop
Long press on timer let you reset or edit timer
swipe on timer text to reset timer (with dialog)
tapping "<" sign on the bottom right corner clears the timer and goes back to Time Selection View.