I don't understand exactly why you would want to do something like this. However, you may be able to accomplish this with a scheduler entry to run at reboot. Have the script it runs disable the secondary interface then "delay" 10 to 60 seconds, whatever you need, before enabling the interface again.
I don't know if the run on reboot script will run before the pppoe interfaces have a chance to come up or not. It may just be a race and you may not be able to reliably determine which will happen first on any particular boot.
I am making the assumption that you want this to happen on boot, rather than every time you lose your connection on pppoe-out1.