How to set the table cells as time format?

[jiaron_1230]

in the column "from" and "to", is let the user to key in their working time, format as 24hr


after that, in std, n/std, n/std2, each of it hv different time area

std= 0800 - 1700
n/std=1701-2400
n/std2=2401-0759

i would like to do is calculate the hours that user had work.
Example,
from to std n/std n/std2
0900 0200 8 7 2

Can anyone help me with this?