It’s 21 to 5 (Official clock system).

04:39

It’s 21 to 5.

Correct answer

04:40

It’s 20 to 5.

Error: 1 minute later

03:53

It’s 7 to 4.

Error: read minutes starting from hour markings and adding minutes

08:20

It’s 20 past 8.

Error: confuse hour and minute hands