Words and Numbers - Quarter Hours

Time may be stated several ways using words. Examples include:

Eight o'clock8:00
Eight forty-five8:45
Forty-five minutes after eight8:45
Forty-five minutes past eight8:45
Forty-five after eight8:45
Forty-five past eight8:45
A quarter past eight8:15
A quarter after eight8:15
Half past eight8:30
Fifteen minutes before nine8:45
Fifteen minutes until nine8:45
Fifteen minutes till nine8:45
A quarter before nine8:45
A quarter until nine8:45
A quarter till nine8:45

What is the Numerical value for the time?