Defalting start time and end time based on absence type selected

Dear all,

Greetings.

I have a doubt in ESS leave request .i will just brief my scenario.

We have 2 absence type APL first half leave and APL second half leave .when user will select the absence

type in leave request according to that start time and end time should get defaulted automatically .I try to  badi PT_ABS_ARQ

but all methods triggers only after clicking on review button.Please give me some hints .I need a BAdI which triggers after selecting absence type .also i want to ask a thing the start time end time is coming defaultly as 1200 to 1200 where we can control that.

Waiting for your valuable inputs.

Thanks.