Use work center absence & Planned (Firm planned /Released) production orders.

Hi Experts,

I use dynamics NAV 2009 R2, I raise this question regarding manufacturing module.

I create a firm planned order from planning worksheet.

When consider routing lines, one work center (WC-A )  its start production 8.00AM to 11.00AM.

But production manager identified labor deficit WC-A can start 9.00AM.

He record that absence in to work center card   (Work center-->Planning-->Absence--> Date= 01/01/2013   Start time=8.00AM End time=9.00AM--> Absence-->Update)

Then planner refresh & re-plan the firm planned order but there is no changes. :(

Can anybody tell us what is the mistake which we did here ?

Thanks in advance :)