Creating a gap function between 2 time stamps and changing that to minutes

Hi,

I am trying to convert a time data type into a gap time. Right now I have 2 time stamps that I can take the difference of to get another "time stamp". I need to convert this to decimal minutes, but I am having trouble using the LEFT and MID functions to do this, possibly because the data is a time type. Is there a way I can change a time data type that displays 00:30:56 to be 30.93? I tried

=IFERROR(((LEFT(H3,2))*60)+(MID(H3,4,2))+((MID(H3,7,2)/60)),0)

But I am not getting the answer I need. If H3 was 00:30:56 in this formula I would get an outcome of 22.35 instead of 30.93. What am I doing wrong? Please help.