Accurate assessment of saliva sampling time is essential for studies that collect cortisol sample in ambulatory settings. This study examined the sampling time assessed by user-submitted photos via a mobile application (ZEMI) compared with MEMSCaps™. Intra-class correlation coefficient (ICC) of the time differences between when the 16 adolescents in the study were prompted to collect the sample and (1) when the MEMSCaps™ was opened (Time[subscript M]), and (2) when photos of the corresponding sample were submitted (Time[subscript Z]) was computed to evaluate the agreement of sampling times. The average Time[subscript M] and Time[subscript Z] 12.06 ± 65.80 and 16.13 ± 52.07 minutes, respectively. The pooled ICC between Time[subscript M] and Time[subscript Z] was 0.986 (95% CI: 0.959-0.995), suggesting excellent correspondence between the two measurements.