change color that depends on remaining time left

hello,

i would like to develop a system where i need to display the case id column and the status.The status column is need to

change the color regarding the remaining time left.
Besides that, each case id have start date/time and end date/time itself.

Here some condition that i need to imlement to this system:

i) if time duration = 30% of original duration, the status bar or color will be green

ii) if time duration = 60% of original duration, the status bar or color will be yellow

iii) if time duration = 100% of original duration, the status bar or color will be red

1) how i need to code and allow user to key in the single textbox field with start date and time together?

2) how i need to code the color of the status change regarding the remaining time left?

Currently i am using php..

can anyone help me please... :)