I understand from AI that the CeCi module utilizes the GPS's clock but the Periodic Survey timestamp is pulled from the internal (Windows CE) clock on the Allegro. The PS timestamp is just as important and should be synced with the built-in GPS time as well.

The Allegro's internal clock can and will drift over time thus making the timestamp unreliable within the Periodic Survey.  This is especially true when using the Allegro and the PCS's Telluric module. The GPS timestamp is imperative for both the readings taken from the Allegro, and the dataloggers used upstream and downstream.  These timestamps must lineup within milliseconds.  A drifting Allegro clock can throw off these readings which would cause issues with the final Telluric compensation calculation.

Therefore, the Periodic Survey's should only sync with the GPS time.

Current rig: Allegro QX.  PS ver: 7.0.0  Windows CE 5.2.29361 (6.5 pro)