Oce 3121 Technical & Service Manual page 507

The distance varies according to the length of the paper.
Note:
Delay at the refeed sensor PS12
A delay will be signalled if the paper does not reach the sensor PS12 within a
specified period of time after the paper passes the sensor PS7.
Timing for the refeed sensor PS12 (overlay copying)
Timing for the refeed sensor PS12 (two-sided copying)
526 TSM Océ 3121 Functional description