[chc]

I don't even understand that. What time period is that meant to specify?

[radnor]

20 to 3 in the afternoon = 2:40 PM

[infogulch]

Oooh, "twenty minutes until three". I typically use until or shorten it to 'till. But I've seen/heard to as well.

[samdb]

'To' is the most common version in British English.