The Digital Timepiece's ADAT sync output defaults to a mode where it always "polls" for an actual ADAT on it's ADAT Sync out. This is an ADAT sync standard, and is typically required for ADAT sync.
The PCI-424 card's ADAT Sync input port does not respond to these "polls" as if it were a true ADAT. So you'll need to make a slight adjustment to the DTP.
Using sequencing software, insert the following sysex message on a midi track, assigning the track to send to the DTP's midi IN port.

F0 00 00 33 20 7f 01 01 03 02 00 40 02 02 01 F7

This message tells the DTP to trasmit sync out of it's ADAT Sync out port without "polling" for an true ADAT.
Once this message is transmitted, It will not have to sent again. The DTP will save this setting (unless it get changed, reset, etc).