My Cisco TA boot time from power-up to the TiVo TA Connected screen is always 15 minutes.
The following should be of some assistance:
Cisco Tuning Adapter Status Troubleshooting
Tuning Adapter Reset:
1. Unplug the USB of the TA to the TiVo
2. Unplug the AC to the TA (not the TiVo)
3. Wait three minutes
4. Plug in the Power to the TA BUT NOT the USB
5. Wait three minutes. The TA should on it's own acquire its IP address (changes in the rate of flashing of the green led from slow to fast).
6. Plug in the USB to the TA from the TiVo
From this point it takes 15 minutes for my TiVos to recognize the TA is connected.
I have had a few occasions where the above steps did not resolve the issue, but holding in the power button on the front for 15 -30 seconds did, so you might give that a shot too.