Please can someone suggest how i could do the following:

In Cells B2:B137 i need to input time in this format hh:mm.

This then needs to be converted to decimal eg 1:30 = 1.5, 45:=0.75

And each value changed as it is added to any of the cells in the range above.

I also only want to work in 15minute segments therefore a time input of 1:24 would need to change to 1:30 and then converted to 1.5 in the cell.
or
a time input of 1:18 would need to change to 1:15 and then converted to 1.25 in the cell.

Please advise...

Many thanks for any help