SAP archive log backup not running on schedule

Hi,

I've a situation here where I have configured a SAP archive log backup. The backup will trigger redo log script in client server and will save and delete to netbackup media. I've set the schedule start open window to  24x7 with frequency every 1 hours.

Now the backup is running successfully, but it not running on time. What I mean that, I want the backup to run exactly on every 2PM, 3PM, 4PM and so on for easier log tracing on SAP in the future. But now it running at 2.30PM, 3.30PM....and sometime 8.50PM, 9.50PM with no accurate time. Please refer below image for the start window setting and attribute setting.

I've checked on all setting, and but there is no setting that can do this. 

Is there any solution for this?

Thanks