On the dot
Definition 1 of 1
Pro Tip 1/3Time Precision
Use 'on the dot' when precise timing is important or expected. 
The webinar will start at 9:00 on the dot, so don't be late.
Pro Tip 2/3Informal Expression
'On the dot' is casual, more common in spoken English or informal writing. 
Can you call me at noon on the dot? We'll catch up quickly.
Pro Tip 3/3Emphasizing Punctuality
Use the phrase to emphasize that someone is always on time. 
He always clocks in at 8 on the dot; he's never late.