“three oh five”
The time 3:05 is read three oh five. For single-digit minutes from 01 to 09, the zero is pronounced oh. For an exact hour, say three o'clock, as in line 2.
A1-54 / CEFR A1 / EPISODE 54
Asking the time and platform
SceneTrying to catch the next train.

WORDS & CONTEXT
The time 3:05 is read three oh five. For single-digit minutes from 01 to 09, the zero is pronounced oh. For an exact hour, say three o'clock, as in line 2.
Here then means "in that case," and faster means more quickly. Fast walking means walking quickly, and that in I can do that. refers to fast walking. The punchline is Frank's literal-minded honesty: he insists he does not run, but he happily agrees to walk fast.