To convert it to a value:
=MINUTE(A1)+(HOUR(A1)*60)
where A1 is the time.

While Mike H's formula (=A1*60*24) would be the quickest method (although I
would change the 60*24 in it to 1440 to save a multiplication), if you
wanted to examine alternate methods, then here is another one to consider
(shorter than yours and one function call less)...

=--TEXT(A1,"[m]")

Rick