The phrase "average time span of" is correct and usable in written English.
It can be used when discussing the typical duration or length of time associated with a particular event or phenomenon.
Example: "The average time span of a human life has increased over the past century due to advancements in healthcare."
Alternatives: "typical duration of" or "mean length of".
The average time span of the measurements was about 5.3 years.
The average time span of the various deployments, primarily designed for surface wave tomography, is 6 months, which is rather limited for shear wave splitting analysis.
The average time span between the activation of the first muscle to the last muscle was 370.2 ms. Five out of 14 subjects exceeded the average time span of 527 ms found in subjects with ankle sprains in the study by Bullock-Saxton et al which was considered to be indicative of an aberrant firing pattern.
The average time span for each patient group to complete all of their visits was 720, 2504 and 5125 days, respectively whereas the average time to complete the first cluster was 357, 1050 and 654 days, respectively.
The average time span between administrations of the L-PAQ was 8 months (range, 2 8)—a longer interval than in previous retest studies of other questionnaires measuring lifetime physical activity, which ranged from 1 week to 8 weeks (3, 4, 9).
The average time span between the occurrence of the injury dispute and closure of claims was 3 years.
The average time span between the two assessments was longer than reported in other validation studies of the MINI.
During a follow up period of 25 months, the average (SD) time span of drug purchase was 11.2 (7.8) months and the nurse documented patient intake for each drug was on average (SD) 14.5 (8.0) months (Table 2).
The baseline was calculated from the blood flow velocity averaged over a time span of 5 seconds before the beginning of the stimulation phase and set to zero.
