Approximate average time in seconds between the end
of integration of each step of the scan and the start
of integration of the next step.
In general, this will agree with
_diffrn_scan_frame.time_rstrt_incr. The
sum of the values of _diffrn_scan_frame.integration_time
and _diffrn_scan_frame.time_rstrt_incr is the
time from the start of integration of one frame and the start of
integration for the next frame and should equal the value of
_diffrn_scan_frame.time_period for this
frame. If the individual frame values vary, then the value of
_diffrn_scan.time_rstrt_incr will be
representative of the ensemble of values of
_diffrn_scan_frame.time_rstrt_incr (e.g.
the mean).