Using Formated Number In Formula

i need to use a cell which has the value 00:30:00 (formated as hh:mm:ss) displayed as 0.020833333 (formated as general)

what i need to do is use the 0.020833333 for a calculation.

now the problem is that i have 00:30:00 as input.

that means the user is inserting 00:30:00 in a cell. i need to convert this to 0.020833333 and use it in a formula

the conversion itself is easy. (just change formating of the cell)

i tried using it like this:
A1: 00:30:00
somenumber<(TEXT($A$1;"##.#########"))
but that gives me strange numbers

and what i need is this:
somenumber<0.020833333)