Guys, this is an easy fix! You can use any timer you want inside a NS Powercenter. Digital, analog, astro... Any make or model will work. I use Aube Ti035 digital astro timers inside with great success. They are robust, relatively low cost, and effective. If you don't have a blank decora style modular bay mounting plate just put the timer inside a single gang device box inside the wiring bay.
The key is knowing which terminals to connect to inside the Powercenter. Just remember that #1 is Line, #2 is Load and #4 is neutral. Use blue crimp on terminals on the timer wires and connect to the power centre terminals. easy.