Time to digital minutes

[ogmium]

I have a spreadsheet that has stumped me maybe someone can help.

The spreadsheet deals with videos and has an extra unit for hours, minutes, seconds and
frames. The last frame is always zero zero as per

01/10/2015 00:00:00:00 00:00:46:00 BEAUTIFUL MUSIC BEAUTIFUL WORLD

Consisting of date, start time, playing time (0hours,0minutes, 46seconds and 00 frames for the title beautiful World.

I wish to import a file which will convert the 00:00:46:00 to digital minutes.
I have tried
=(HOUR(RC[-5]) * 60 + MINUTE(RC[-5]) + SECOND(RC[-5]) / 60)/60 but it does not work?

The field is formatted as a 'general' format at source

Any help appreciated

regards
ogmium