Basic start/finish time in CO01

Dear Experts,

I'm using scheduling type 'only capacity requirements.' Whenever I'm creating a production order basic start/finish dates can be changed but not the time.Time field is un-editable for both basic start time and basic finish time. (Start 00:00   Finish 24:00) 

I need to manually enter  some value to these two time fields. How this can be done? Please give your valuable ideas.

Regards,

Jeewana