This is a reference list, not a lesson with exercises — browse each group, read the meaning and example, and come back whenever you need a natural way to talk about time.
Exact time
sharp
exactly at the stated time
The meeting starts at 9:00 sharp.
on the dot
exactly; not a minute early or late
The train left at 8:15 on the dot.
to the minute
with perfect precision
He arrived at 6:00 to the minute.
to the second
accurate to the exact second
The rocket launched to the second.
right on time
perfectly punctual
You were right on time.
bang on (UK)
exactly
She arrived bang on six.
dead on (US)
exactly
The clock struck twelve dead on.
promptly
punctually; formal
The ceremony begins promptly at 7:00.
Approximate time
about
approximately
About six.
around
approximately
Around six.
roughly
approximately
Roughly six o'clock.
approximately
formal approximation
Approximately six.
or so
approximately
Six or so.
give or take
plus or minus a little
Six, give or take a few minutes.
-ish
informal suffix meaning approximately
Six-ish.
Just in time / Late / Early
just in time
at the last possible moment
We got there just in time.
at the last minute
very late, just before a deadline
She arrived at the last minute.
in the nick of time
idiom: just before it was too late
We caught the train in the nick of time.
ahead of time
earlier than necessary
We arrived ahead of time.
ahead of schedule
earlier than planned
The project finished ahead of schedule.
behind schedule
later than planned
The project is behind schedule.
running late
being late
Sorry, I'm running late.
running behind
falling behind schedule
I'm running behind.
Literary
at the stroke of midnight
exactly when the clock strikes midnight
The magic ended at the stroke of midnight.
at the stroke of noon
exactly at noon
The ceremony began at the stroke of noon.
when the clock struck…
narrative expression
When the clock struck six…
Military / Aviation
at oh-six-hundred
military pronunciation of 06:00
Report at oh-six-hundred.
at zero six hundred hours
full military form
Meet at zero six hundred hours.
at eighteen hundred
18:00
Departure at eighteen hundred.
at twenty-three hundred hours
23:00
Lights out at twenty-three hundred hours.
The 10 natives actually use most:
sharp · on the dot · right on time · just in time · ahead of time · running late · behind schedule · ahead of schedule · in the nick of time · six-ish