Need a formula to change a negative time to negative decimal

Hi,

I have some data imported from a .csv file. If I import the data in general negative time numbers get a circular reference (i.e they get imported as =-17:50).

If I import everything as text it displays all the numbers correctly. Now I want to convert the time to decimals. So 08:12 is returned as 8,20 and 34:30 is returned 34,50.
Normally I would just use =A1*24 to get the decimal value but if the time number is negative this returns #VALUE!

I found this formula that works (I have no idea exactly what it does but it works)

=SUBSTITUTE(C2;"-";"")*24*SIGN(LEFT(A2;2)+0)

This formula does indeed return decimal value from both positive and negative time numbers. Great! But the negative time number is returned as a positive decimal number.

Anyone have a solution so that I can return a negative decimal value from a negative time value?

Thanks